Hi,
I have also worked with 7PDF a while ago. On windows 7 with MS Office 2013, everything was fine, but migrated to Windows 2012 and I had same troubles like you. Sorry, but this is the true.
In one of my posts, Mark gave a hint about PDFCombinePROX (command line, not cheap but powerful, the producer says its a server solution). Also I have abandoned MS Office because converting is too slow (7->10 seconds). Yes you can have processes in background, but even than if you have a fast user, the system is not fast enough. So, now I'm using HTML reports, much faster and also good looking (a little css work have to be done, but the web is full of examples). A report in HTML is almost instant and with PDFCombinePROX you can combine multiple file types (docx, hrml, pdf, etc.)
https://forum.awareim.com/d/7799/18&hilit=office#p33021
Hope this helps,