Welcome to the Make community!
You’ll have to download as PDF to upload to OpenAI “Message an Assistant” module.
For more information, see How to PDF into openAI (Solution!)
Otherwise, you can also use CloudConvert to convert it to a TEXT file, so that you can paste the text contents of the file directly into the prompt.
Hope this helps! Let me know if there are any further questions or issues.
— @samliew
P.S.: Investing some effort into the Make Academy will save you lots of time and frustration using Make.