One thing that using Linux has taught me is to always look for the simplest solution, because it probably exists. As it turned out in this case.
In this case, I was emailed a five page PDF document that I had to print, sign, scan and send back. Printing and signing, of course, was easy enough and I can scan the five pages to get five, separate PDF files. Merging these files back into a single document is where pdfunite comes in, and it really is as simple as:
pdfunite page1.pdf page2.pdf page3.pdf page4.pdf page5.pdf outfile.pdf
You can specify as many source files as you like and the last file is the destination file.
And if I’d known about pdfseperate, I could have probably avoided printing the entire document in the first place.