I am unable to combine PDF files. I'll get the error "The document could not be saved. This file is already open or in use by another application." No other application has it open. If I copy the file from the network location to the local hard drive I am able to combine the file. I've tried multiple different PDFs on the network drive all with the same results.
We are sorry for the trouble. As described, you are unable to combine the PDFs on network locations while it works fine when downloading the files to the computer local drive.
It seems to be some issue with your network settings. Please check the network and group policy settings at your end.
You may also try to turn off the protected mode for testing purposes. Go to Edit (Windows), Adobe Acrobat DC (Mac) > Preferences > Enhanced Security > Trun off the protected mode and uncheck the enhanced security > Click OK and reboot the application. Note: Please turn on the security after testing.
You may also try to add the file and the network folder to the white list in Adobe Acrobat application. Go to Edit (Windows), Adobe Acrobat DC (Mac) > Preferences > Enhanced Security > Add File and Add Folder Path. > Relaunch the application and check.