diff --git a/homeassistant/components/openai_conversation/__init__.py b/homeassistant/components/openai_conversation/__init__.py
index 06a61d70b011..b4c9a16693a3 100644
--- a/homeassistant/components/openai_conversation/__init__.py
+++ b/homeassistant/components/openai_conversation/__init__.py
@@ -148,7 +148,7 @@ async def async_setup(hass: HomeAssistant, config: ConfigType) -> bool:
 
             content.extend(
                 await async_prepare_files_for_prompt(
-                    hass, [Path(filename) for filename in filenames]
+                    hass, [(Path(filename), None) for filename in filenames]
                 )
             )
 
diff --git a/homeassistant/components/openai_conversation/entity.py b/homeassistant/components/openai_conversation/entity.py
index 95311830ec94..4d2c62a7a8c2 100644
--- a/homeassistant/components/openai_conversation/entity.py
+++ b/homeassistant/components/openai_conversation/entity.py
@@ -223,15 +223,17 @@ def _convert_content_to_param(
                     ResponseReasoningItemParam(
                         type="reasoning",
                         id=content.native.id,
-                        summary=[
-                            {
-                                "type": "summary_text",
-                                "text": summary,
-                            }
-                            for summary in reasoning_summary
-                        ]
-                        if content.thinking_content
-                        else [],
+                        summary=(
+                            [
+                                {
+                                    "type": "summary_text",
+                                    "text": summary,
+                                }
+                                for summary in reasoning_summary
+                            ]
+                            if content.thinking_content
+                            else []
+                        ),
                         encrypted_content=content.native.encrypted_content,
                     )
                 )
@@ -308,9 +310,11 @@ async def _transform_stream(  # noqa: C901 - This is complex, but better to have
                     "tool_call_id": event.item.id,
                     "tool_name": "code_interpreter",
                     "tool_result": {
-                        "output": [output.to_dict() for output in event.item.outputs]  # type: ignore[misc]
-                        if event.item.outputs is not None
-                        else None
+                        "output": (
+                            [output.to_dict() for output in event.item.outputs]  # type: ignore[misc]
+                            if event.item.outputs is not None
+                            else None
+                        )
                     },
                 }
                 last_role = "tool_result"
@@ -529,7 +533,7 @@ class OpenAIBaseLLMEntity(Entity):
         if last_content.role == "user" and last_content.attachments:
             files = await async_prepare_files_for_prompt(
                 self.hass,
-                [a.path for a in last_content.attachments],
+                [(a.path, a.mime_type) for a in last_content.attachments],
             )
             last_message = messages[-1]
             assert (
@@ -601,7 +605,7 @@ class OpenAIBaseLLMEntity(Entity):
 
 
 async def async_prepare_files_for_prompt(
-    hass: HomeAssistant, files: list[Path]
+    hass: HomeAssistant, files: list[tuple[Path, str | None]]
 ) -> ResponseInputMessageContentListParam:
     """Append files to a prompt.
 
@@ -611,11 +615,12 @@ async def async_prepare_files_for_prompt(
     def append_files_to_content() -> ResponseInputMessageContentListParam:
         content: ResponseInputMessageContentListParam = []
 
-        for file_path in files:
+        for file_path, mime_type in files:
             if not file_path.exists():
                 raise HomeAssistantError(f"`{file_path}` does not exist")
 
-            mime_type, _ = guess_file_type(file_path)
+            if mime_type is None:
+                mime_type = guess_file_type(file_path)[0]
 
             if not mime_type or not mime_type.startswith(("image/", "application/pdf")):
                 raise HomeAssistantError(
diff --git a/tests/components/openai_conversation/test_ai_task.py b/tests/components/openai_conversation/test_ai_task.py
index 51ac505893e1..b9a69e5f77ed 100644
--- a/tests/components/openai_conversation/test_ai_task.py
+++ b/tests/components/openai_conversation/test_ai_task.py
@@ -155,14 +155,13 @@ async def test_generate_data_with_attachments(
                     path=Path("doorbell_snapshot.jpg"),
                 ),
                 media_source.PlayMedia(
-                    url="http://example.com/context.txt",
-                    mime_type="text/plain",
-                    path=Path("context.txt"),
+                    url="http://example.com/context.pdf",
+                    mime_type="application/pdf",
+                    path=Path("context.pdf"),
                 ),
             ],
         ),
         patch("pathlib.Path.exists", return_value=True),
-        # patch.object(hass.config, "is_allowed_path", return_value=True),
         patch(
             "homeassistant.components.openai_conversation.entity.guess_file_type",
             return_value=("image/jpeg", None),
@@ -176,7 +175,7 @@ async def test_generate_data_with_attachments(
             instructions="Test prompt",
             attachments=[
                 {"media_content_id": "media-source://media/doorbell_snapshot.jpg"},
-                {"media_content_id": "media-source://media/context.txt"},
+                {"media_content_id": "media-source://media/context.pdf"},
             ],
         )
 
@@ -205,9 +204,9 @@ async def test_generate_data_with_attachments(
             "type": "input_image",
         },
         {
-            "detail": "auto",
-            "image_url": "data:image/jpeg;base64,ZmFrZV9pbWFnZV9kYXRh",
-            "type": "input_image",
+            "filename": "context.pdf",
+            "file_data": "data:application/pdf;base64,ZmFrZV9pbWFnZV9kYXRh",
+            "type": "input_file",
         },
     ]