Is there a way to add a cover to a .pdf file in the Windows Kindle app?

Why do you say they do not have cover art? did you use the left arrow to go back from the first page through the TOC to the cover?

Are you looking at the sample works or other works you have downloaded?

I will be making heavy use of this soon as I work on taking my friend’s book from print to Kindle.

Otherwise—do you have Adobe Acrobat? That is the best program for working on PDF files?

@anartist . . . The covers don’t appear when I’m viewing the library.

I just downloaded the program and am looking at it. Send me the file if you want. Maybe I can add it in Acrobbat. I’m going to be learning how to work with this el-fasto.
Do you see a TOC? [table of contents]

Jon try this https://read.amazon.com/?asin=B004LX069M the answer may be here
But possibly the author didn’t load a cover—a lot of newbie kindle publishers.
The instructions for formatting and uploading are several pages in

I noticed in the instructions that uploading a cover is optional.

Yes of course you can add a cover to a PDF or ePub.

how-to-add-cover-to-epub

But here I recommend you to read them on your PC with PDF reader such as Adobe Reader instead of the Kindle app. Because Kindle app just recognize the Kindle format files such as mobi.

Maybe you can convert PDF to MOBI.