Merge 2 documents with Adobe

[Pierre5FE2]

Each time I try to merge two documents it is impposible to go to the end of the process. I Just keep receiving an error message. Saying it's impossible

[Karl Heinz Kremer]

What is the exact error message? One of these files may be corrupt. Open each file on its own and then do a File>Save As (it needs to be a "save as", it behaves differently than the normal 'save'). Does that result in an error mesasge? Do you have Acrobat Pro? If so, you can use the Preflight tool to test the files for PDF errors. 

[try67]

Also, what's the exact version number of the application (You can find it out by going to Help - About Adobe Acrobat)? What's your OS version?