I don’t believe Webflow has the capability you’re looking for – there is no way to create a download button.
However, several people have asked how to do this, and this is the best answer I’ve found: Want to create a link to download a PDF - General - Forum | Webflow
So, you upload the file to DropBox, get the link from DropBox, insert the link in Webflow, and change the link so the final “0” is a “1.”
I’ve used this method, and it works just fine.
Hope that works for you! 