diff --git a/.changes/unreleased/Fixed-20251003-130249.yaml b/.changes/unreleased/Fixed-20251003-130249.yaml
new file mode 100644
index 000000000..b6db3cafc
--- /dev/null
+++ b/.changes/unreleased/Fixed-20251003-130249.yaml
@@ -0,0 +1,6 @@
+kind: Fixed
+body: Add exception handling for conversion of attachment on sending external, when documens are already in pdf
+time: 2025-10-03T13:02:49.524835257+02:00
+custom:
+    Issue: ""
+    SchemaChange: No schema change
diff --git a/src/Bundle/ChillDocStoreBundle/Exception/ConversionWithSameMimeTypeException.php b/src/Bundle/ChillDocStoreBundle/Exception/ConversionWithSameMimeTypeException.php
new file mode 100644
index 000000000..06fb4a9ed
--- /dev/null
+++ b/src/Bundle/ChillDocStoreBundle/Exception/ConversionWithSameMimeTypeException.php
@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * Chill is a software for social workers
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+namespace Chill\DocStoreBundle\Exception;
+
+class ConversionWithSameMimeTypeException extends \RuntimeException
+{
+    public function __construct(string $mimeType, ?\Throwable $previous = null)
+    {
+        parent::__construct("Conversion to same MIME type '{$mimeType}' is not allowed: already at the same MIME type", 0, $previous);
+    }
+}
diff --git a/src/Bundle/ChillDocStoreBundle/Service/StoredObjectToPdfConverter.php b/src/Bundle/ChillDocStoreBundle/Service/StoredObjectToPdfConverter.php
index ac570c513..8a5ea6e8c 100644
--- a/src/Bundle/ChillDocStoreBundle/Service/StoredObjectToPdfConverter.php
+++ b/src/Bundle/ChillDocStoreBundle/Service/StoredObjectToPdfConverter.php
@@ -15,6 +15,7 @@ use Chill\DocStoreBundle\Entity\StoredObject;
 use Chill\DocStoreBundle\Entity\StoredObjectPointInTime;
 use Chill\DocStoreBundle\Entity\StoredObjectPointInTimeReasonEnum;
 use Chill\DocStoreBundle\Entity\StoredObjectVersion;
+use Chill\DocStoreBundle\Exception\ConversionWithSameMimeTypeException;
 use Chill\DocStoreBundle\Exception\StoredObjectManagerException;
 use Chill\WopiBundle\Service\WopiConverter;
 use Symfony\Component\Mime\MimeTypesInterface;
@@ -41,9 +42,10 @@ class StoredObjectToPdfConverter
      *
      * @return array{0: StoredObjectPointInTime, 1: StoredObjectVersion, 2?: string} contains the point in time before conversion and the new version of the stored object. The converted content is included in the response if $includeConvertedContent is true
      *
-     * @throws \UnexpectedValueException    if the preferred mime type for the conversion is not found
-     * @throws \RuntimeException            if the conversion or storage of the new version fails
+     * @throws \UnexpectedValueException           if the preferred mime type for the conversion is not found
+     * @throws \RuntimeException                   if the conversion or storage of the new version fails
      * @throws StoredObjectManagerException
+     * @throws ConversionWithSameMimeTypeException if the document has already the same mime type79*
      */
     public function addConvertedVersion(StoredObject $storedObject, string $lang, $convertTo = 'pdf', bool $includeConvertedContent = false): array
     {
@@ -56,7 +58,7 @@ class StoredObjectToPdfConverter
         $currentVersion = $storedObject->getCurrentVersion();
 
         if ($currentVersion->getType() === $newMimeType) {
-            throw new \UnexpectedValueException('Already at the same mime type');
+            throw new ConversionWithSameMimeTypeException($newMimeType);
         }
 
         $content = $this->storedObjectManager->read($currentVersion);
diff --git a/src/Bundle/ChillMainBundle/Workflow/Messenger/PostSendExternalMessageHandler.php b/src/Bundle/ChillMainBundle/Workflow/Messenger/PostSendExternalMessageHandler.php
index 66888cce6..2e5f74808 100644
--- a/src/Bundle/ChillMainBundle/Workflow/Messenger/PostSendExternalMessageHandler.php
+++ b/src/Bundle/ChillMainBundle/Workflow/Messenger/PostSendExternalMessageHandler.php
@@ -11,6 +11,7 @@ declare(strict_types=1);
 
 namespace Chill\MainBundle\Workflow\Messenger;
 
+use Chill\DocStoreBundle\Exception\ConversionWithSameMimeTypeException;
 use Chill\DocStoreBundle\Exception\StoredObjectManagerException;
 use Chill\DocStoreBundle\Service\StoredObjectToPdfConverter;
 use Chill\MainBundle\Entity\Workflow\EntityWorkflow;
@@ -55,6 +56,8 @@ final readonly class PostSendExternalMessageHandler implements MessageHandlerInt
                 $this->storedObjectToPdfConverter->addConvertedVersion($attachment->getProxyStoredObject(), $locale);
             } catch (StoredObjectManagerException $e) {
                 $this->logger->error('Error converting attachment to PDF', ['backtrace' => $e->getTraceAsString(), 'attachment_id' => $attachment->getId()]);
+            } catch (ConversionWithSameMimeTypeException $e) {
+                $this->logger->error('Error converting attachment to PDF: already at the same MIME type', ['backtrace' => $e->getTraceAsString(), 'attachment_id' => $attachment->getId()]);
             }
         }
 
@@ -65,6 +68,8 @@ final readonly class PostSendExternalMessageHandler implements MessageHandlerInt
                 $this->storedObjectToPdfConverter->addConvertedVersion($storedObject, $locale);
             } catch (StoredObjectManagerException $e) {
                 $this->logger->error('Error converting stored object to PDF', ['backtrace' => $e->getTraceAsString(), 'stored_object_id' => $storedObject->getId(), 'workflow_id' => $entityWorkflow->getId()]);
+            } catch (ConversionWithSameMimeTypeException $e) {
+                $this->logger->error('Error converting stored object to PDF: already at the same MIME type', ['backtrace' => $e->getTraceAsString(), 'stored_object_id' => $storedObject->getId(), 'workflow_id' => $entityWorkflow->getId()]);
             }
         }
     }