You see the error message File Type Not Supported when you try to upload a document to Copilot in Microsoft 365 Chat or Copilot in Word. This error occurs because Copilot can only process a specific set of file formats for grounding and content generation. The file you are uploading uses an extension or encoding that Copilot does not recognize. This article explains which file types Copilot supports, why the error appears, and how to convert or re-save your file so the upload succeeds.
Key Takeaways: Supported File Types for Copilot Uploads
- Accepted formats: Copilot accepts .docx, .xlsx, .pptx, .pdf, .txt, .csv, and .html files. All other extensions trigger the error.
- Convert using Microsoft 365 apps: Open the unsupported file in its native application and use Save As to choose an accepted format such as .docx or .pdf.
- Check file encoding: Plain text files must be UTF-8 or ASCII. Files saved in UTF-16 or other encodings may be rejected even if the extension is .txt.
Why Copilot Rejects Certain File Types
Copilot relies on Microsoft Graph and the Microsoft 365 document processing pipeline to extract text and structure from uploaded files. The pipeline includes parsers optimized for Office Open XML formats .docx, .xlsx, .pptx and for standard web and plain-text formats .html, .txt, .csv. PDF files are processed through a separate OCR and text-extraction engine. Any file type outside this list, such as .odt, .rtf, .pages, .key, .zip, or image-only formats like .jpg and .png, does not have a corresponding parser in the Copilot ingestion service. The service returns the File Type Not Supported error instead of attempting a conversion. File size also matters: the maximum upload size is 512 MB per file. Files larger than that may also fail with a generic error, though the message sometimes reads File Type Not Supported if the size check fails early in the pipeline.
File Encoding Restrictions for Text and CSV Files
Even when the file extension is .txt or .csv, Copilot may reject the upload if the file is saved with a non-standard encoding. The ingestion service expects UTF-8 with BOM or UTF-8 without BOM. UTF-16 Little Endian and UTF-16 Big Endian files are common in legacy systems and can cause the parser to misread the byte order mark. In that case the service treats the file as corrupted and returns the same File Type Not Supported error. You can check encoding in Notepad by opening the file and looking at the Encoding field in the Save As dialog.
Steps to Fix the File Type Not Supported Error
Follow these steps to convert your file to a supported format and upload it to Copilot without errors.
- Identify the file extension
Right-click the file in File Explorer and select Properties. Look at the Type of file field. If the extension is not .docx, .xlsx, .pptx, .pdf, .txt, .csv, or .html, you must convert it. - Open the file in its native application
Launch the program that created the file. For example, open a .odt file in LibreOffice Writer, a .pages file in Apple Pages, or a .rtf file in WordPad or Microsoft Word. - Use Save As to change the format
Go to File > Save As. In the Save as type dropdown, choose a supported format. For documents, select Word Document .docx. For spreadsheets, select Excel Workbook .xlsx. For presentations, select PowerPoint Presentation .pptx. For any file, you can also select PDF .pdf. - Re-save the file with a new name
Click Save. The new file will have the correct extension and encoding. Close the original unsupported file. - Upload the converted file to Copilot
In Microsoft 365 Chat, click the paperclip icon and select the newly saved file. In Copilot in Word, go to References > Copilot > Upload File. The error should no longer appear.
Fix Encoding for Text and CSV Files
- Open the file in Notepad
Right-click the .txt or .csv file and choose Open with > Notepad. - Check the current encoding
Click File > Save As. Look at the Encoding dropdown at the bottom of the dialog. If it shows UTF-16 LE or UTF-16 BE, proceed to the next step. - Change encoding to UTF-8
In the Encoding dropdown, select UTF-8. Do not select UTF-8 with BOM unless Copilot still rejects the file after the change. - Save the file with a new name
Type a new file name and click Save. Close Notepad. Upload the new file to Copilot.
If Copilot Still Shows the Error After Conversion
Some files trigger the error even after you change the extension and encoding. The following scenarios are the most common.
File Is Password-Protected or Encrypted
Copilot cannot open files that require a password or that use Microsoft Information Protection encryption. Remove any password protection before uploading. In Word, go to File > Info > Protect Document > Encrypt with Password and delete the password. Save the file again and upload it.
File Exceeds the 512 MB Size Limit
Copilot rejects files larger than 512 MB. Check the file size in File Explorer. If the file exceeds the limit, split the content into smaller files. For a large PDF, use the Split PDF tool in Adobe Acrobat or a free online service. Upload each part separately.
File Contains Only Images With No Selectable Text
A PDF that is a scanned image with no embedded text will fail because Copilot cannot extract content from image-only files. Use a PDF OCR tool such as Microsoft Lens or Adobe Acrobat to convert the scanned pages to selectable text. Save the result as a new PDF and upload that file.
File Uses a Non-Standard Extension That Matches a Supported Type
Some applications save files with a supported extension but use a non-standard internal format. For example, a .docx file created by a third-party word processor may not follow the Office Open XML schema. Open the file in Microsoft Word. If Word shows a conversion warning, let it repair the file. Then save the file again as .docx.
Supported File Types vs Unsupported File Types
| Category | Supported Formats | Unsupported Formats |
|---|---|---|
| Documents | .docx, .pdf, .txt, .html | .odt, .rtf, .pages, .wps, .doc |
| Spreadsheets | .xlsx, .csv | .ods, .numbers, .xls, .slk |
| Presentations | .pptx | .odp, .key, .ppt, .pps |
| Other | None | .zip, .jpg, .png, .gif, .mp3, .mp4, .msg, .eml |
Copilot also does not support files stored on third-party cloud services like Google Drive or Dropbox unless you first download the file to your local device and then upload it through the Microsoft 365 interface. Files attached to Outlook emails must be saved locally before uploading.
You can now identify the exact cause of the File Type Not Supported error and convert any file to a format that Copilot accepts. Use the Save As method in the original application to change the extension, and verify text file encoding in Notepad. For persistent failures, check password protection, file size, and text extractability. As a next step, try uploading a .docx file that contains structured headings and tables to see how Copilot uses the document structure to generate grounded responses.