diff --git a/docling/datamodel/document.py b/docling/datamodel/document.py
index 2b3aa9b..984cf02 100644
--- a/docling/datamodel/document.py
+++ b/docling/datamodel/document.py
@@ -302,7 +302,7 @@ class _DocumentConversionInput(BaseModel):
                     if ("." in obj.name and not obj.name.startswith("."))
                     else ""
                 )
-                mime = _DocumentConversionInput._mime_from_extension(ext)
+                mime = _DocumentConversionInput._mime_from_extension(ext.lower())
             if mime is not None and mime.lower() == "application/zip":
                 objname = obj.name.lower()
                 if objname.endswith(".xlsx"):
@@ -376,6 +376,13 @@ class _DocumentConversionInput(BaseModel):
             mime = FormatToMimeType[InputFormat.JSON_DOCLING][0]
         elif ext in FormatToExtensions[InputFormat.PDF]:
             mime = FormatToMimeType[InputFormat.PDF][0]
+        elif ext in FormatToExtensions[InputFormat.DOCX]:
+            mime = FormatToMimeType[InputFormat.DOCX][0]
+        elif ext in FormatToExtensions[InputFormat.PPTX]:
+            mime = FormatToMimeType[InputFormat.PPTX][0]
+        elif ext in FormatToExtensions[InputFormat.XLSX]:
+            mime = FormatToMimeType[InputFormat.XLSX][0]
+
         return mime
 
     @staticmethod