File extraction error, can't combine files

I am trying to combine 2 .pdfs into one. I open my Acrobat Reader, choose combine, and upload the files online. It says there is an extraction error and won't combine.

I have read multiple posts here with suggestions - use Acrobat, not reader, but my version is Acrobat Reader. I've converted the file to a Word document then reconverted. I've checked for updates. I've rebooted my computer. Nothing works.

Any suggestions?