Combining PDFs Tells Me Unsupported Files

[nmrozek]

I'm trying to combine two PDF files into one using Acrobat DC. I tried both "Combine Files" and "Organize Pages", but I'm told they are unsupported file types despite both being .pdf

[try67]

They may be secured, digitally signed, created in LiveCycle Designer, etc.

[Harlean]

I want to recommend "Combine PDF" online tools first because online services are more convenient compared to desktop applications. The best “Combine PDF” tool I have used is EasePDF. EasePDF is a cross-platform supported online PDF service, which offers lots of basic PDF editing, converting, and creating tools.

[Bernd Alheit]

The most companies doesn't allow the use of online services.