Hello! I am having a problem combining files in Adobe - none are password protected and I'm just combining six pdf files none of which are large files. I have a paid subscription, and this is puzzling me as I have never had an issue like this in the past.
Sorry for the trouble.
Are you using Acrobat Pro DC or Acrobat Pro 2020? If you choose another set of files are you experiencing the same issue?
Also, try creating a PDF file using Acrobat and check if that is working without an issue? In the meantime, if you have an Acrobat Pro DC subscription, you may try combining via browser using Acrobat Online services: https://documentcloud.adobe.com/