Download error - MIME type

I have added many pages to Cloudflare and noticed a disturbing thing. I run an e-shop and many products have an attached file such as instructions in the .pdf file format. After adding the site to Cloudflare, attachments stopped working.
After Initiating the download however, the file is not downloaded and a message appears “Interrupted: network error” is displayed. In the chrome browser specifically in the console a warning message appears: “Resource interpreted as Document but transferred with MIME type application / octet-stream”. Please help me in this matter, and tell me how to unlock the downloading process.
Thank you