diff --git a/app/MindWork AI Studio/Assistants/I18N/allTexts.lua b/app/MindWork AI Studio/Assistants/I18N/allTexts.lua
index 9fc9540a..75137ecd 100644
--- a/app/MindWork AI Studio/Assistants/I18N/allTexts.lua	
+++ b/app/MindWork AI Studio/Assistants/I18N/allTexts.lua	
@@ -7753,6 +7753,9 @@ UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T29806295
 -- Images are not supported at this place
 UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T305247150"] = "Images are not supported at this place"
 
+-- This file format is not supported. Please convert the .doc file to .docx (e.g. with Microsoft Word).
+UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T3740637731"] = "This file format is not supported. Please convert the .doc file to .docx (e.g. with Microsoft Word)."
+
 -- Unsupported file type
 UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T4041351522"] = "Unsupported file type"
 
diff --git a/app/MindWork AI Studio/Plugins/languages/de-de-43065dbc-78d0-45b7-92be-f14c2926e2dc/plugin.lua b/app/MindWork AI Studio/Plugins/languages/de-de-43065dbc-78d0-45b7-92be-f14c2926e2dc/plugin.lua
index 90a16a92..d79e6f5c 100644
--- a/app/MindWork AI Studio/Plugins/languages/de-de-43065dbc-78d0-45b7-92be-f14c2926e2dc/plugin.lua	
+++ b/app/MindWork AI Studio/Plugins/languages/de-de-43065dbc-78d0-45b7-92be-f14c2926e2dc/plugin.lua	
@@ -7746,6 +7746,9 @@ UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T13982828
 -- File has no extension
 UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T1555980031"] = "Datei hat keine Erweiterung"
 
+-- This file format is not supported.
+UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T2634293666"] = "Dieses Dateiformat wird nicht unterstützt. Bitte konvertieren Sie die .doc-Datei in .docx (z. B. mit Microsoft Word)."
+
 -- Audio files are not supported yet
 UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T2919730669"] = "Audio-Dateien werden noch nicht unterstützt."
 
diff --git a/app/MindWork AI Studio/Plugins/languages/en-us-97dfb1ba-50c4-4440-8dfa-6575daf543c8/plugin.lua b/app/MindWork AI Studio/Plugins/languages/en-us-97dfb1ba-50c4-4440-8dfa-6575daf543c8/plugin.lua
index 742e8525..2cfa7dca 100644
--- a/app/MindWork AI Studio/Plugins/languages/en-us-97dfb1ba-50c4-4440-8dfa-6575daf543c8/plugin.lua	
+++ b/app/MindWork AI Studio/Plugins/languages/en-us-97dfb1ba-50c4-4440-8dfa-6575daf543c8/plugin.lua	
@@ -7758,6 +7758,9 @@ UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T29806295
 -- Images are not supported at this place
 UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T305247150"] = "Images are not supported at this place"
 
+-- This file format is not supported.
+UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T1506058512"] = "This file format is not supported. Please convert the .doc file to .docx (e.g. with Microsoft Word)."
+
 -- Unsupported file type
 UI_TEXT_CONTENT["AISTUDIO::TOOLS::VALIDATION::FILEEXTENSIONVALIDATION::T4041351522"] = "Unsupported file type"
 
@@ -7807,4 +7810,4 @@ UI_TEXT_CONTENT["AISTUDIO::TOOLS::WORKSPACEBEHAVIOUR::T1307384014"] = "Unnamed w
 UI_TEXT_CONTENT["AISTUDIO::TOOLS::WORKSPACEBEHAVIOUR::T2244038752"] = "Delete Chat"
 
 -- Unnamed chat
-UI_TEXT_CONTENT["AISTUDIO::TOOLS::WORKSPACEBEHAVIOUR::T3310482275"] = "Unnamed chat"
+UI_TEXT_CONTENT["AISTUDIO::TOOLS::WORKSPACEBEHAVIOUR::T3310482275"] = "Unnamed chat"
\ No newline at end of file
diff --git a/app/MindWork AI Studio/Tools/Rust/FileTypes.cs b/app/MindWork AI Studio/Tools/Rust/FileTypes.cs
index ebd62c5e..b53f5146 100644
--- a/app/MindWork AI Studio/Tools/Rust/FileTypes.cs	
+++ b/app/MindWork AI Studio/Tools/Rust/FileTypes.cs	
@@ -45,7 +45,7 @@ public static class FileTypes
     // Document hierarchy
     public static readonly FileTypeFilter PDF         = FileTypeFilter.Leaf("PDF", "pdf");
     public static readonly FileTypeFilter TEXT        = FileTypeFilter.Leaf(TB("Text"), "txt", "md", "rtf");
-    public static readonly FileTypeFilter MS_WORD     = FileTypeFilter.Leaf("Microsoft Word", "docx", "doc");
+    public static readonly FileTypeFilter MS_WORD     = FileTypeFilter.Leaf("Microsoft Word", "docx");
     public static readonly FileTypeFilter WORD        = FileTypeFilter.Composite("Word", ["odt"], MS_WORD);
     public static readonly FileTypeFilter EXCEL       = FileTypeFilter.Leaf("Excel", "xls", "xlsx");
     public static readonly FileTypeFilter POWER_POINT = FileTypeFilter.Leaf("PowerPoint", "ppt", "pptx");
diff --git a/app/MindWork AI Studio/Tools/Validation/FileExtensionValidation.cs b/app/MindWork AI Studio/Tools/Validation/FileExtensionValidation.cs
index efecce3d..2251ecd5 100644
--- a/app/MindWork AI Studio/Tools/Validation/FileExtensionValidation.cs	
+++ b/app/MindWork AI Studio/Tools/Validation/FileExtensionValidation.cs	
@@ -43,6 +43,14 @@ public static class FileExtensionValidation
     /// <returns>True if valid, false if invalid (error/warning already sent via MessageBus).</returns>
     public static async Task<bool> IsExtensionValidWithNotifyAsync(UseCase useCae, string filePath, bool validateMediaFileTypes = true, Settings.Provider? provider = null)
     {
+        if (string.Equals(Path.GetExtension(filePath), ".doc", StringComparison.OrdinalIgnoreCase))
+        {
+            await MessageBus.INSTANCE.SendWarning(new(
+                Icons.Material.Filled.Description,
+                TB("This file format is not supported. Please convert the .doc file to .docx (e.g. with Microsoft Word).")));
+            return false;
+        }
+
         if (FileTypes.IsAllowedPath(filePath, FileTypes.EXECUTABLES))
         {
             await MessageBus.INSTANCE.SendError(new(
@@ -138,4 +146,4 @@ public static class FileExtensionValidation
 
         return true;
     }
-}
+}
\ No newline at end of file
diff --git a/app/MindWork AI Studio/wwwroot/changelog/v26.5.5.md b/app/MindWork AI Studio/wwwroot/changelog/v26.5.5.md
index 2620bda9..1a1d45e3 100644
--- a/app/MindWork AI Studio/wwwroot/changelog/v26.5.5.md	
+++ b/app/MindWork AI Studio/wwwroot/changelog/v26.5.5.md	
@@ -10,6 +10,7 @@
 - Improved the Qdrant startup and vector database initialization, so AI Studio can start more reliably while the local vector database is still starting.
 - Fixed the Pandoc installation, which could fail and prevent AI Studio from installing its local Pandoc dependency.
 - Fixed an issue where the spellchecking setting was not applied to all text fields in the slide builder assistant.
+- Fixed an issue where legacy `.doc` files could be selected even though AI Studio could not process them. These files are now rejected with a clear error message. Thanks to Bernhard for reporting this issue.
 - Fixed missing translations for file type names in file selection dialogs.
 - Upgraded the native secret storage integration to `keyring-core`, keeping API keys in the secure credential store provided by the operating system.
 - Upgraded Rust to v1.95.0.