diff --git a/src/Clients/CreditNote.php b/src/Clients/CreditNote.php
index e613f13..9f087f3 100644
--- a/src/Clients/CreditNote.php
+++ b/src/Clients/CreditNote.php
@@ -7,6 +7,7 @@
 use Sysix\LexOffice\BaseClient;
 use Sysix\LexOffice\Clients\Traits\CreateFinalizeTrait;
 use Sysix\LexOffice\Clients\Traits\DocumentClientTrait;
+use Sysix\LexOffice\Clients\Traits\FileClientWithAcceptHeaderTrait;
 use Sysix\LexOffice\Clients\Traits\GetTrait;
 use Sysix\LexOffice\Clients\Traits\PursueFinalizeTrait;
 use Sysix\LexOffice\Clients\Traits\VoucherListTrait;
@@ -15,6 +16,7 @@ class CreditNote extends BaseClient
 {
     use CreateFinalizeTrait;
     use DocumentClientTrait;
+    use FileClientWithAcceptHeaderTrait;
     use GetTrait;
     use PursueFinalizeTrait;
     use VoucherListTrait;
diff --git a/src/Clients/DeliveryNote.php b/src/Clients/DeliveryNote.php
index 80be06b..5bfee9a 100644
--- a/src/Clients/DeliveryNote.php
+++ b/src/Clients/DeliveryNote.php
@@ -7,6 +7,7 @@
 use Sysix\LexOffice\BaseClient;
 use Sysix\LexOffice\Clients\Traits\CreateTrait;
 use Sysix\LexOffice\Clients\Traits\DocumentClientTrait;
+use Sysix\LexOffice\Clients\Traits\FileClientTrait;
 use Sysix\LexOffice\Clients\Traits\GetTrait;
 use Sysix\LexOffice\Clients\Traits\PursueTrait;
 use Sysix\LexOffice\Clients\Traits\VoucherListTrait;
@@ -15,6 +16,7 @@ class DeliveryNote extends BaseClient
 {
     use CreateTrait;
     use DocumentClientTrait;
+    use FileClientTrait;
     use GetTrait;
     use PursueTrait;
     use VoucherListTrait;
diff --git a/src/Clients/DownPaymentInvoice.php b/src/Clients/DownPaymentInvoice.php
index f227be3..353a20d 100644
--- a/src/Clients/DownPaymentInvoice.php
+++ b/src/Clients/DownPaymentInvoice.php
@@ -6,12 +6,14 @@
 
 use Sysix\LexOffice\BaseClient;
 use Sysix\LexOffice\Clients\Traits\DocumentClientTrait;
+use Sysix\LexOffice\Clients\Traits\FileClientWithAcceptHeaderTrait;
 use Sysix\LexOffice\Clients\Traits\GetTrait;
 use Sysix\LexOffice\Clients\Traits\VoucherListTrait;
 
 class DownPaymentInvoice extends BaseClient
 {
     use DocumentClientTrait;
+    use FileClientWithAcceptHeaderTrait;
     use GetTrait;
     use VoucherListTrait;
 
diff --git a/src/Clients/Dunning.php b/src/Clients/Dunning.php
index fedb58b..fc72d4c 100644
--- a/src/Clients/Dunning.php
+++ b/src/Clients/Dunning.php
@@ -6,12 +6,14 @@
 
 use Sysix\LexOffice\BaseClient;
 use Sysix\LexOffice\Clients\Traits\DocumentClientTrait;
+use Sysix\LexOffice\Clients\Traits\FileClientTrait;
 use Sysix\LexOffice\Clients\Traits\GetTrait;
 use Sysix\LexOffice\Clients\Traits\PursueTrait;
 
 class Dunning extends BaseClient
 {
     use DocumentClientTrait;
+    use FileClientTrait;
     use GetTrait;
     use PursueTrait;
 
diff --git a/src/Clients/Invoice.php b/src/Clients/Invoice.php
index ce2b039..b45108e 100644
--- a/src/Clients/Invoice.php
+++ b/src/Clients/Invoice.php
@@ -7,6 +7,7 @@
 use Sysix\LexOffice\BaseClient;
 use Sysix\LexOffice\Clients\Traits\CreateFinalizeTrait;
 use Sysix\LexOffice\Clients\Traits\DocumentClientTrait;
+use Sysix\LexOffice\Clients\Traits\FileClientWithAcceptHeaderTrait;
 use Sysix\LexOffice\Clients\Traits\GetTrait;
 use Sysix\LexOffice\Clients\Traits\PursueFinalizeTrait;
 use Sysix\LexOffice\Clients\Traits\VoucherListTrait;
@@ -15,6 +16,7 @@ class Invoice extends BaseClient
 {
     use CreateFinalizeTrait;
     use DocumentClientTrait;
+    use FileClientWithAcceptHeaderTrait;
     use GetTrait;
     use PursueFinalizeTrait;
     use VoucherListTrait;
diff --git a/src/Clients/OrderConfirmation.php b/src/Clients/OrderConfirmation.php
index 393d9f1..f64a31b 100644
--- a/src/Clients/OrderConfirmation.php
+++ b/src/Clients/OrderConfirmation.php
@@ -7,6 +7,7 @@
 use Sysix\LexOffice\BaseClient;
 use Sysix\LexOffice\Clients\Traits\CreateTrait;
 use Sysix\LexOffice\Clients\Traits\DocumentClientTrait;
+use Sysix\LexOffice\Clients\Traits\FileClientTrait;
 use Sysix\LexOffice\Clients\Traits\GetTrait;
 use Sysix\LexOffice\Clients\Traits\PursueTrait;
 use Sysix\LexOffice\Clients\Traits\VoucherListTrait;
@@ -15,6 +16,7 @@ class OrderConfirmation extends BaseClient
 {
     use CreateTrait;
     use DocumentClientTrait;
+    use FileClientTrait;
     use GetTrait;
     use PursueTrait;
     use VoucherListTrait;
diff --git a/src/Clients/Quotation.php b/src/Clients/Quotation.php
index 992c2ac..bd35a90 100644
--- a/src/Clients/Quotation.php
+++ b/src/Clients/Quotation.php
@@ -7,6 +7,7 @@
 use Sysix\LexOffice\BaseClient;
 use Sysix\LexOffice\Clients\Traits\CreateFinalizeTrait;
 use Sysix\LexOffice\Clients\Traits\DocumentClientTrait;
+use Sysix\LexOffice\Clients\Traits\FileClientTrait;
 use Sysix\LexOffice\Clients\Traits\GetTrait;
 use Sysix\LexOffice\Clients\Traits\VoucherListTrait;
 
@@ -14,6 +15,7 @@ class Quotation extends BaseClient
 {
     use CreateFinalizeTrait;
     use DocumentClientTrait;
+    use FileClientTrait;
     use GetTrait;
     use VoucherListTrait;
 
diff --git a/src/Clients/Traits/DocumentClientTrait.php b/src/Clients/Traits/DocumentClientTrait.php
index 97572bb..b02d525 100644
--- a/src/Clients/Traits/DocumentClientTrait.php
+++ b/src/Clients/Traits/DocumentClientTrait.php
@@ -7,12 +7,10 @@
 use Psr\Http\Message\ResponseInterface;
 
 /**
- * @deprecated use the FileClientTrait instead
+ * @deprecated use the FileClientTrait or FileClientWithAcceptHeaderTrait instead
  */
 trait DocumentClientTrait
 {
-    use FileClientTrait;
-
     public function document(string $id, bool $asContent = false, string $acceptHeader = '*/*'): ResponseInterface
     {
         trigger_error(__METHOD__.' should not be called anymore, in future versions this method WILL not exist', E_USER_DEPRECATED);
@@ -25,6 +23,10 @@ public function document(string $id, bool $asContent = false, string $acceptHead
             return $response;
         }
 
-        return $this->file($id, $acceptHeader);
+        $this->api->newRequest('GET', $this->resource . '/' . rawurlencode($id) . '/file');
+
+        return $this->api
+            ->setRequest($this->api->getRequest()->withHeader('Accept', $acceptHeader))
+            ->getResponse();
     }
 }
diff --git a/src/Clients/Traits/FileClientTrait.php b/src/Clients/Traits/FileClientTrait.php
index 1b1664f..40de862 100644
--- a/src/Clients/Traits/FileClientTrait.php
+++ b/src/Clients/Traits/FileClientTrait.php
@@ -8,12 +8,12 @@
 
 trait FileClientTrait
 {
-    public function file(string $id, string $acceptHeader = '*/*'): ResponseInterface
+    public function file(string $id): ResponseInterface
     {
         $this->api->newRequest('GET', $this->resource . '/' . rawurlencode($id) . '/file');
 
         return $this->api
-            ->setRequest($this->api->getRequest()->withHeader('Accept', $acceptHeader))
+            ->setRequest($this->api->getRequest()->withHeader('Accept', '*/*'))
             ->getResponse();
     }
 }
diff --git a/src/Clients/Traits/FileClientWithAcceptHeaderTrait.php b/src/Clients/Traits/FileClientWithAcceptHeaderTrait.php
new file mode 100644
index 0000000..ea85f45
--- /dev/null
+++ b/src/Clients/Traits/FileClientWithAcceptHeaderTrait.php
@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sysix\LexOffice\Clients\Traits;
+
+use Psr\Http\Message\ResponseInterface;
+
+trait FileClientWithAcceptHeaderTrait
+{
+    public function file(string $id, string $acceptHeader = '*/*'): ResponseInterface
+    {
+        $this->api->newRequest('GET', $this->resource . '/' . rawurlencode($id) . '/file');
+
+        return $this->api
+            ->setRequest($this->api->getRequest()->withHeader('Accept', $acceptHeader))
+            ->getResponse();
+    }
+}
diff --git a/src/Utils.php b/src/Utils.php
index a669f58..afdd8d9 100644
--- a/src/Utils.php
+++ b/src/Utils.php
@@ -83,7 +83,7 @@ public static function createStream(mixed $content): StreamInterface
      *
      * @param array<string, string|bool|resource> $content
      */
-    public static function createMultipartStream(array $content, string $boundary = null): MultipartStream
+    public static function createMultipartStream(array $content, ?string $boundary = null): MultipartStream
     {
         $stream = [];
         $boundary = !is_null($boundary) && $boundary !== '' ? $boundary : '--lexoffice';
diff --git a/tests/Clients/CreditNoteTest.php b/tests/Clients/CreditNoteTest.php
index 7f4754d..ec8dc10 100644
--- a/tests/Clients/CreditNoteTest.php
+++ b/tests/Clients/CreditNoteTest.php
@@ -184,6 +184,29 @@ public function testFileContent(): void
         $this->assertInstanceOf(ResponseInterface::class, $response);
 
         $this->assertEquals('GET', $api->getRequest()->getMethod());
+        $this->assertEquals(
+            '*/*',
+            $api->getRequest()->getHeaderLine('Accept')
+        );
+        $this->assertEquals(
+            $api->apiUrl . '/v1/credit-notes/resource-id/file',
+            $api->getRequest()->getUri()->__toString()
+        );
+    }
+
+    public function testFileContentWithAcceptHeader(): void
+    {
+        [$api, $stub] = $this->createClientMockObject(CreditNote::class);
+
+        $response = $stub->file('resource-id', 'application/xml');
+
+        $this->assertInstanceOf(ResponseInterface::class, $response);
+
+        $this->assertEquals('GET', $api->getRequest()->getMethod());
+        $this->assertEquals(
+            'application/xml',
+            $api->getRequest()->getHeaderLine('Accept')
+        );
         $this->assertEquals(
             $api->apiUrl . '/v1/credit-notes/resource-id/file',
             $api->getRequest()->getUri()->__toString()
diff --git a/tests/Clients/DownPaymentInvoiceTest.php b/tests/Clients/DownPaymentInvoiceTest.php
index 24361ce..649e8ef 100644
--- a/tests/Clients/DownPaymentInvoiceTest.php
+++ b/tests/Clients/DownPaymentInvoiceTest.php
@@ -99,6 +99,29 @@ public function testFileContent(): void
         $this->assertInstanceOf(ResponseInterface::class, $response);
 
         $this->assertEquals('GET', $api->getRequest()->getMethod());
+        $this->assertEquals(
+            '*/*',
+            $api->getRequest()->getHeaderLine('Accept')
+        );
+        $this->assertEquals(
+            $api->apiUrl . '/v1/down-payment-invoices/resource-id/file',
+            $api->getRequest()->getUri()->__toString()
+        );
+    }
+
+    public function testFileContentWithAcceptHeader(): void
+    {
+        [$api, $stub] = $this->createClientMockObject(DownPaymentInvoice::class);
+
+        $response = $stub->file('resource-id', 'application/xml');
+
+        $this->assertInstanceOf(ResponseInterface::class, $response);
+
+        $this->assertEquals('GET', $api->getRequest()->getMethod());
+        $this->assertEquals(
+            'application/xml',
+            $api->getRequest()->getHeaderLine('Accept')
+        );
         $this->assertEquals(
             $api->apiUrl . '/v1/down-payment-invoices/resource-id/file',
             $api->getRequest()->getUri()->__toString()
diff --git a/tests/Clients/InvoiceTest.php b/tests/Clients/InvoiceTest.php
index 2384738..7a0a389 100644
--- a/tests/Clients/InvoiceTest.php
+++ b/tests/Clients/InvoiceTest.php
@@ -184,9 +184,33 @@ public function testFileContent(): void
         $this->assertInstanceOf(ResponseInterface::class, $response);
 
         $this->assertEquals('GET', $api->getRequest()->getMethod());
+        $this->assertEquals(
+            '*/*',
+            $api->getRequest()->getHeaderLine('Accept')
+        );
+        $this->assertEquals(
+            $api->apiUrl . '/v1/invoices/resource-id/file',
+            $api->getRequest()->getUri()->__toString()
+        );
+    }
+
+    public function testFileContentWithAcceptHeader(): void
+    {
+        [$api, $stub] = $this->createClientMockObject(Invoice::class);
+
+        $response = $stub->file('resource-id', 'application/xml');
+
+        $this->assertInstanceOf(ResponseInterface::class, $response);
+
+        $this->assertEquals('GET', $api->getRequest()->getMethod());
+        $this->assertEquals(
+            'application/xml',
+            $api->getRequest()->getHeaderLine('Accept')
+        );
         $this->assertEquals(
             $api->apiUrl . '/v1/invoices/resource-id/file',
             $api->getRequest()->getUri()->__toString()
         );
     }
+
 }