This tool is similar to my Acrobat -- Batch Combine All PDF Files in a Folder script, only it's not a script, it's a more robust stand-alone tool that does the same task but is capable of processing more files quicker and more efficiently.

The tool looks like this:

The applications' GUI (click to enlarge)



If you wish to test the tool before purchasing it, a free demo version is available here.
The demo version is limited to processing up to 3 files in up to 3 folders. The full version has no such limits, of course.https://try67.blogspot.com/2015/03/batch-combine-all-pdf-files-in-folders.html