diff --git a/src/Dto/DeductionDocumentData.php b/src/Dto/DeductionDocumentData.php
new file mode 100644
index 0000000..a8be218
--- /dev/null
+++ b/src/Dto/DeductionDocumentData.php
@@ -0,0 +1,22 @@
+<?php
+
+// SPDX-FileCopyrightText: 2026 LibreCode coop and contributors
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+declare(strict_types=1);
+
+namespace LibreCodeCoop\NfsePHP\Dto;
+
+final readonly class DeductionDocumentData
+{
+    public function __construct(
+        public DeductionDocumentReferenceData $reference,
+        public int $type,
+        public string $issuedAt,
+        public string $deductibleValue,
+        public string $deductionValue,
+        public string $otherDescription = '',
+        public ?DeductionSupplierData $supplier = null,
+    ) {
+    }
+}
diff --git a/src/Dto/DeductionDocumentReferenceData.php b/src/Dto/DeductionDocumentReferenceData.php
new file mode 100644
index 0000000..2169f0e
--- /dev/null
+++ b/src/Dto/DeductionDocumentReferenceData.php
@@ -0,0 +1,58 @@
+<?php
+
+// SPDX-FileCopyrightText: 2026 LibreCode coop and contributors
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+declare(strict_types=1);
+
+namespace LibreCodeCoop\NfsePHP\Dto;
+
+/**
+ * One of the mutually exclusive document identities accepted by TCDocDedRed.
+ */
+final readonly class DeductionDocumentReferenceData
+{
+    private function __construct(
+        public string $type,
+        public array $values,
+    ) {
+    }
+
+    public static function nfse(string $accessKey): self
+    {
+        return new self('nfse', ['access_key' => $accessKey]);
+    }
+
+    public static function nfe(string $accessKey): self
+    {
+        return new self('nfe', ['access_key' => $accessKey]);
+    }
+
+    public static function legacyNfse(string $municipioIbge, string $numero, string $codigoVerificacao): self
+    {
+        return new self('legacy_nfse', [
+            'municipio_ibge' => $municipioIbge,
+            'numero' => $numero,
+            'codigo_verificacao' => $codigoVerificacao,
+        ]);
+    }
+
+    public static function legacyNfNfs(string $numero, string $modelo, string $serie): self
+    {
+        return new self('legacy_nf_nfs', [
+            'numero' => $numero,
+            'modelo' => $modelo,
+            'serie' => $serie,
+        ]);
+    }
+
+    public static function fiscalDocument(string $numero): self
+    {
+        return new self('fiscal_document', ['numero' => $numero]);
+    }
+
+    public static function document(string $numero): self
+    {
+        return new self('document', ['numero' => $numero]);
+    }
+}
diff --git a/src/Dto/DeductionReductionData.php b/src/Dto/DeductionReductionData.php
index 433959f..40d97d7 100644
--- a/src/Dto/DeductionReductionData.php
+++ b/src/Dto/DeductionReductionData.php
@@ -15,9 +15,13 @@
  */
 final readonly class DeductionReductionData
 {
+    /**
+     * @param list<DeductionDocumentData> $documentos
+     */
     public function __construct(
         public string $percentual = '',
         public string $valor = '',
+        public array $documentos = [],
     ) {
     }
 }
diff --git a/src/Dto/DeductionSupplierData.php b/src/Dto/DeductionSupplierData.php
new file mode 100644
index 0000000..d398a50
--- /dev/null
+++ b/src/Dto/DeductionSupplierData.php
@@ -0,0 +1,27 @@
+<?php
+
+// SPDX-FileCopyrightText: 2026 LibreCode coop and contributors
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+declare(strict_types=1);
+
+namespace LibreCodeCoop\NfsePHP\Dto;
+
+/**
+ * Optional supplier identity used by a document-backed deduction.
+ *
+ * Address data is intentionally omitted because TCInfoPessoa makes it optional.
+ */
+final readonly class DeductionSupplierData
+{
+    public function __construct(
+        public string $identityType,
+        public string $identity,
+        public string $name,
+        public string $caepf = '',
+        public string $municipalRegistration = '',
+        public string $phone = '',
+        public string $email = '',
+    ) {
+    }
+}
diff --git a/src/Xml/XmlBuilder.php b/src/Xml/XmlBuilder.php
index 99c1826..ed6499d 100644
--- a/src/Xml/XmlBuilder.php
+++ b/src/Xml/XmlBuilder.php
@@ -271,10 +271,12 @@ private function buildDeductionReduction(\DOMDocument $doc, DpsData $dps): \DOME
 
         $hasPercentage = $deduction->percentual !== '';
         $hasValue = $deduction->valor !== '';
+        $hasDocuments = $deduction->documentos !== [];
+        $modeCount = (int) $hasPercentage + (int) $hasValue + (int) $hasDocuments;
 
-        if ($hasPercentage === $hasValue) {
+        if ($modeCount !== 1) {
             throw new \InvalidArgumentException(
-                'Deduction/reduction must provide exactly one of percentual (pDR) or valor (vDR).',
+                'Deduction/reduction must provide exactly one of percentual (pDR), valor (vDR) or documentos.',
             );
         }
 
@@ -283,14 +285,184 @@ private function buildDeductionReduction(\DOMDocument $doc, DpsData $dps): \DOME
         if ($hasPercentage) {
             $this->assertDecimal($deduction->percentual, 3, 'Deduction/reduction percentage');
             $vDedRed->appendChild($doc->createElement('pDR', $deduction->percentual));
-        } else {
+
+            return $vDedRed;
+        }
+
+        if ($hasValue) {
             $this->assertDecimal($deduction->valor, 15, 'Deduction/reduction value');
             $vDedRed->appendChild($doc->createElement('vDR', $deduction->valor));
+
+            return $vDedRed;
+        }
+
+        if (count($deduction->documentos) > 1000) {
+            throw new \InvalidArgumentException('Deduction/reduction supports at most 1000 documents.');
         }
 
+        $documents = $doc->createElement('documentos');
+
+        foreach ($deduction->documentos as $document) {
+            $documents->appendChild($this->buildDeductionDocument($doc, $document));
+        }
+
+        $vDedRed->appendChild($documents);
+
         return $vDedRed;
     }
 
+    private function buildDeductionDocument(
+        \DOMDocument $doc,
+        \LibreCodeCoop\NfsePHP\Dto\DeductionDocumentData $document,
+    ): \DOMElement {
+        if (!in_array($document->type, [1, 2, 3, 4, 5, 6, 7, 8, 9, 99], true)) {
+            throw new \InvalidArgumentException('Deduction document type must be 1-9 or 99.');
+        }
+
+        if ($document->type === 99 && trim($document->otherDescription) === '') {
+            throw new \InvalidArgumentException('Other deduction type (99) requires a description.');
+        }
+
+        if ($document->type !== 99 && $document->otherDescription !== '') {
+            throw new \InvalidArgumentException('Other deduction description is only allowed for type 99.');
+        }
+
+        $date = \DateTimeImmutable::createFromFormat('!Y-m-d', $document->issuedAt);
+        if ($date === false || $date->format('Y-m-d') !== $document->issuedAt) {
+            throw new \InvalidArgumentException('Deduction document issue date must use YYYY-MM-DD.');
+        }
+
+        $this->assertDecimal($document->deductibleValue, 15, 'Deductible/reducible document value');
+        $this->assertDecimal($document->deductionValue, 15, 'Applied deduction/reduction value');
+
+        if ((float) $document->deductionValue > (float) $document->deductibleValue) {
+            throw new \InvalidArgumentException(
+                'Applied deduction/reduction value cannot exceed the deductible/reducible document value.',
+            );
+        }
+
+        $element = $doc->createElement('docDedRed');
+        $element->appendChild($this->buildDeductionDocumentReference($doc, $document->reference));
+        $element->appendChild($doc->createElement('tpDedRed', (string) $document->type));
+
+        if ($document->otherDescription !== '') {
+            $element->appendChild(
+                $doc->createElement('xDescOutDed', htmlspecialchars($document->otherDescription, ENT_XML1)),
+            );
+        }
+
+        $element->appendChild($doc->createElement('dtEmiDoc', $document->issuedAt));
+        $element->appendChild($doc->createElement('vDedutivelRedutivel', $document->deductibleValue));
+        $element->appendChild($doc->createElement('vDeducaoReducao', $document->deductionValue));
+
+        if ($document->supplier !== null) {
+            $element->appendChild($this->buildDeductionSupplier($doc, $document->supplier));
+        }
+
+        return $element;
+    }
+
+    private function buildDeductionDocumentReference(
+        \DOMDocument $doc,
+        \LibreCodeCoop\NfsePHP\Dto\DeductionDocumentReferenceData $reference,
+    ): \DOMElement {
+        return match ($reference->type) {
+            'nfse' => $doc->createElement('chNFSe', (string) ($reference->values['access_key'] ?? '')),
+            'nfe' => $doc->createElement('chNFe', (string) ($reference->values['access_key'] ?? '')),
+            'legacy_nfse' => $this->buildLegacyNfseReference($doc, $reference->values),
+            'legacy_nf_nfs' => $this->buildLegacyNfNfsReference($doc, $reference->values),
+            'fiscal_document' => $doc->createElement('nDocFisc', (string) ($reference->values['numero'] ?? '')),
+            'document' => $doc->createElement('nDoc', (string) ($reference->values['numero'] ?? '')),
+            default => throw new \InvalidArgumentException('Unsupported deduction document reference type.'),
+        };
+    }
+
+    /**
+     * @param array<string, mixed> $values
+     */
+    private function buildLegacyNfseReference(\DOMDocument $doc, array $values): \DOMElement
+    {
+        $group = $doc->createElement('NFSeMun');
+        $group->appendChild($doc->createElement('cMunNFSeMun', (string) ($values['municipio_ibge'] ?? '')));
+        $group->appendChild($doc->createElement('nNFSeMun', (string) ($values['numero'] ?? '')));
+        $group->appendChild($doc->createElement('cVerifNFSeMun', (string) ($values['codigo_verificacao'] ?? '')));
+
+        return $group;
+    }
+
+    /**
+     * @param array<string, mixed> $values
+     */
+    private function buildLegacyNfNfsReference(\DOMDocument $doc, array $values): \DOMElement
+    {
+        $group = $doc->createElement('NFNFS');
+        $group->appendChild($doc->createElement('nNFS', (string) ($values['numero'] ?? '')));
+        $group->appendChild($doc->createElement('modNFS', (string) ($values['modelo'] ?? '')));
+        $group->appendChild($doc->createElement('serieNFS', (string) ($values['serie'] ?? '')));
+
+        return $group;
+    }
+
+    private function buildDeductionSupplier(
+        \DOMDocument $doc,
+        \LibreCodeCoop\NfsePHP\Dto\DeductionSupplierData $supplier,
+    ): \DOMElement {
+        if (trim($supplier->name) === '') {
+            throw new \InvalidArgumentException('Deduction supplier name is required.');
+        }
+
+        $element = $doc->createElement('fornec');
+
+        switch ($supplier->identityType) {
+            case 'cnpj':
+                if (preg_match('/^[A-Z0-9]{12}\d{2}$/', strtoupper($supplier->identity)) !== 1) {
+                    throw new \InvalidArgumentException('Deduction supplier CNPJ must contain 14 valid-format characters.');
+                }
+                $element->appendChild($doc->createElement('CNPJ', strtoupper($supplier->identity)));
+                break;
+            case 'cpf':
+                if (preg_match('/^\d{11}$/', $supplier->identity) !== 1) {
+                    throw new \InvalidArgumentException('Deduction supplier CPF must contain 11 digits.');
+                }
+                $element->appendChild($doc->createElement('CPF', $supplier->identity));
+                break;
+            case 'nif':
+                if ($supplier->identity === '') {
+                    throw new \InvalidArgumentException('Deduction supplier NIF cannot be empty.');
+                }
+                $element->appendChild($doc->createElement('NIF', $supplier->identity));
+                break;
+            case 'no_nif':
+                if (!in_array($supplier->identity, ['0', '1', '2'], true)) {
+                    throw new \InvalidArgumentException('Deduction supplier cNaoNIF must be 0, 1 or 2.');
+                }
+                $element->appendChild($doc->createElement('cNaoNIF', $supplier->identity));
+                break;
+            default:
+                throw new \InvalidArgumentException('Unsupported deduction supplier identity type.');
+        }
+
+        if ($supplier->caepf !== '') {
+            $element->appendChild($doc->createElement('CAEPF', $supplier->caepf));
+        }
+
+        if ($supplier->municipalRegistration !== '') {
+            $element->appendChild($doc->createElement('IM', $supplier->municipalRegistration));
+        }
+
+        $element->appendChild($doc->createElement('xNome', htmlspecialchars($supplier->name, ENT_XML1)));
+
+        if ($supplier->phone !== '') {
+            $element->appendChild($doc->createElement('fone', $supplier->phone));
+        }
+
+        if ($supplier->email !== '') {
+            $element->appendChild($doc->createElement('email', htmlspecialchars($supplier->email, ENT_XML1)));
+        }
+
+        return $element;
+    }
+
     private function buildMunicipalBenefit(\DOMDocument $doc, DpsData $dps): \DOMElement
     {
         $benefit = $dps->beneficioMunicipal;
diff --git a/tests/Unit/Xml/OfficialDpsSchemaValidationTest.php b/tests/Unit/Xml/OfficialDpsSchemaValidationTest.php
index b72e665..310d6af 100644
--- a/tests/Unit/Xml/OfficialDpsSchemaValidationTest.php
+++ b/tests/Unit/Xml/OfficialDpsSchemaValidationTest.php
@@ -7,7 +7,10 @@
 
 namespace LibreCodeCoop\NfsePHP\Tests\Unit\Xml;
 
+use LibreCodeCoop\NfsePHP\Dto\DeductionDocumentData;
+use LibreCodeCoop\NfsePHP\Dto\DeductionDocumentReferenceData;
 use LibreCodeCoop\NfsePHP\Dto\DeductionReductionData;
+use LibreCodeCoop\NfsePHP\Dto\DeductionSupplierData;
 use LibreCodeCoop\NfsePHP\Dto\DpsData;
 use LibreCodeCoop\NfsePHP\Dto\MunicipalBenefitData;
 use LibreCodeCoop\NfsePHP\Dto\SubstitutionData;
@@ -53,6 +56,29 @@ public function testStandardDeductionAndMunicipalBenefitMatchOfficialSchema(): v
         self::assertSame([], $this->validator->validate($xml));
     }
 
+    public function testDocumentBackedDeductionMatchesOfficialSchema(): void
+    {
+        $xml = $this->builder->buildDps($this->makeDps(
+            deducaoReducao: new DeductionReductionData(documentos: [
+                new DeductionDocumentData(
+                    reference: DeductionDocumentReferenceData::document('DOC-2026-001'),
+                    type: 99,
+                    issuedAt: '2026-09-30',
+                    deductibleValue: '500.00',
+                    deductionValue: '125.00',
+                    otherDescription: 'Despesa comprovada',
+                    supplier: new DeductionSupplierData(
+                        identityType: 'cnpj',
+                        identity: '11222333000181',
+                        name: 'Fornecedor Exemplo',
+                    ),
+                ),
+            ]),
+        ));
+
+        self::assertSame([], $this->validator->validate($xml));
+    }
+
     public function testValidatorRejectsUnsupportedSchemaVersionExplicitly(): void
     {
         $this->expectException(\InvalidArgumentException::class);
diff --git a/tests/Unit/Xml/XmlBuilderTest.php b/tests/Unit/Xml/XmlBuilderTest.php
index f7a7e85..48da978 100644
--- a/tests/Unit/Xml/XmlBuilderTest.php
+++ b/tests/Unit/Xml/XmlBuilderTest.php
@@ -7,7 +7,10 @@
 
 namespace LibreCodeCoop\NfsePHP\Tests\Unit\Xml;
 
+use LibreCodeCoop\NfsePHP\Dto\DeductionDocumentData;
+use LibreCodeCoop\NfsePHP\Dto\DeductionDocumentReferenceData;
 use LibreCodeCoop\NfsePHP\Dto\DeductionReductionData;
+use LibreCodeCoop\NfsePHP\Dto\DeductionSupplierData;
 use LibreCodeCoop\NfsePHP\Dto\DpsData;
 use LibreCodeCoop\NfsePHP\Dto\MunicipalBenefitData;
 use LibreCodeCoop\NfsePHP\Dto\SubstitutionData;
@@ -817,6 +820,74 @@ public function testBuildDpsRejectsInvalidMunicipalBenefitIdentifier(): void
         ));
     }
 
+    public function testBuildDpsEmitsDocumentBackedDeductionWithSupplier(): void
+    {
+        $document = new DeductionDocumentData(
+            reference: DeductionDocumentReferenceData::document('DOC-2026-001'),
+            type: 99,
+            issuedAt: '2026-09-30',
+            deductibleValue: '500.00',
+            deductionValue: '125.00',
+            otherDescription: 'Despesa comprovada',
+            supplier: new DeductionSupplierData(
+                identityType: 'cnpj',
+                identity: '11222333000181',
+                name: 'Fornecedor Exemplo',
+            ),
+        );
+
+        $xml = $this->builder->buildDps($this->makeDps(
+            deducaoReducao: new DeductionReductionData(documentos: [$document]),
+        ));
+        $compactXml = preg_replace('/>\s+</', '><', $xml) ?? $xml;
+
+        self::assertStringContainsString(
+            '<documentos><docDedRed><nDoc>DOC-2026-001</nDoc><tpDedRed>99</tpDedRed>'
+            . '<xDescOutDed>Despesa comprovada</xDescOutDed><dtEmiDoc>2026-09-30</dtEmiDoc>'
+            . '<vDedutivelRedutivel>500.00</vDedutivelRedutivel>'
+            . '<vDeducaoReducao>125.00</vDeducaoReducao><fornec>'
+            . '<CNPJ>11222333000181</CNPJ><xNome>Fornecedor Exemplo</xNome></fornec>'
+            . '</docDedRed></documentos>',
+            $compactXml,
+        );
+    }
+
+    public function testBuildDpsRejectsAppliedDeductionAboveDocumentValue(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('cannot exceed');
+
+        $this->builder->buildDps($this->makeDps(
+            deducaoReducao: new DeductionReductionData(documentos: [
+                new DeductionDocumentData(
+                    reference: DeductionDocumentReferenceData::fiscalDocument('NF-123'),
+                    type: 2,
+                    issuedAt: '2026-09-30',
+                    deductibleValue: '100.00',
+                    deductionValue: '101.00',
+                ),
+            ]),
+        ));
+    }
+
+    public function testBuildDpsRejectsOtherDeductionWithoutDescription(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('requires a description');
+
+        $this->builder->buildDps($this->makeDps(
+            deducaoReducao: new DeductionReductionData(documentos: [
+                new DeductionDocumentData(
+                    reference: DeductionDocumentReferenceData::document('DOC-1'),
+                    type: 99,
+                    issuedAt: '2026-09-30',
+                    deductibleValue: '100.00',
+                    deductionValue: '50.00',
+                ),
+            ]),
+        ));
+    }
+
     private function makeDps(
         string $cnpjPrestador = '11222333000181',
         string $municipioIbge = '3303302',