If the issue still persists, please connect the computer to a different network environment like a wired/wireless guest network or a mobile hotspot and try combining the files.
Reboot the machine and try combining the files. If you are using the freeware Adobe Reader DC and facing the issue, please sign out and sign back in Adobe Reader using your Adobe ID and password and then check for any pending updates of Adobe Reader from help>check for updates. Try clearing the cache, cookies, temp files of the browser and see if this brings any difference. The record shows that you are subscribed to Adobe PDFPack subscription, try combining the PDF files with the URL with your Adobe ID and password on a browser like Chrome, or Firefox, or Safari.
We apologize for the inconvenience caused, as per the description above, you are not able to combine the PDF file as getting an error message, is that correct?
