diff --git a/packages/core/src/session/runner/to-llm-message.ts b/packages/core/src/session/runner/to-llm-message.ts
index 698af2795cb..5ff3b166f84 100644
--- a/packages/core/src/session/runner/to-llm-message.ts
+++ b/packages/core/src/session/runner/to-llm-message.ts
@@ -67,7 +67,7 @@ const directoryAttachment = (file: FileAttachment): ContentPart => ({
 const attachmentContent = (file: FileAttachment): ContentPart[] => {
   if (file.mime === "text/plain") return [textAttachment(file)]
   if (file.mime === "application/x-directory") return [directoryAttachment(file)]
-  if (imageMimes.has(file.mime)) {
+  if (imageMimes.has(file.mime) || file.mime === "application/pdf") {
     const location = attachmentLocation(file)
     return [...(location === undefined ? [] : [Message.text(`Attached file: ${location}`)]), media(file)]
   }
diff --git a/packages/core/test/session-model-request.test.ts b/packages/core/test/session-model-request.test.ts
index e2c77ed69ce..f87ab1e085a 100644
--- a/packages/core/test/session-model-request.test.ts
+++ b/packages/core/test/session-model-request.test.ts
@@ -9,16 +9,18 @@ describe("SessionModelRequest.unsupportedParts", () => {
     const messages = unsupportedParts(
       [
         Message.user([
-          Message.text("Describe this image"),
+          Message.text("Describe these files"),
           { type: "media", mediaType: "image/png", data: "aGVsbG8=", filename: "logo.png" },
+          { type: "media", mediaType: "application/pdf", data: "JVBERg==", filename: "document.pdf" },
         ]),
       ],
       capabilities(["text"]),
     )
 
     expect(messages[0]?.content).toEqual([
-      Message.text("Describe this image"),
+      Message.text("Describe these files"),
       Message.text('ERROR: Cannot read "logo.png" (this model does not support image input). Inform the user.'),
+      Message.text('ERROR: Cannot read "document.pdf" (this model does not support pdf input). Inform the user.'),
     ])
   })
 
diff --git a/packages/core/test/session-runner-message.test.ts b/packages/core/test/session-runner-message.test.ts
index a3a677329c4..9adfeb371b5 100644
--- a/packages/core/test/session-runner-message.test.ts
+++ b/packages/core/test/session-runner-message.test.ts
@@ -361,7 +361,7 @@ Recent work
     ])
   })
 
-  test("uses materialized image data as provider media and drops unsupported attachments", () => {
+  test("uses materialized image and PDF data as provider media", () => {
     const data = Base64.make("AAECAw==")
     const messages = toLLMMessages(
       [
@@ -387,6 +387,7 @@ Recent work
     expect(messages[0]?.content).toEqual([
       { type: "text", text: "Inspect this image" },
       { type: "media", mediaType: "image/png", data, filename: "image.png" },
+      { type: "media", mediaType: "application/pdf", data: "JVBERg==", filename: "document.pdf" },
     ])
   })