Hi gina_hall_7848,
If you're combining both Word and PDF files into PDF, there is some conversion happening (with the Word docs, as they're converted into the combined PDF file). If you're getting the error when combining only PDF files--that's another story. It could be that one or more of the files that you're combining isn't in a supported format, or that Adobe PDF Pack is timing out before it can complete the conversion.
Does the error occur regardless of what files you try to combine?
Best,
Sara