Ah, to clarify, I meant the original PDF page size. For example, I have a PDF manual for the Siglent SDS2000X plus, and my PDF reader says (in File -> Properties) that the page size is "8.27 x 11.68 in. (A4)". If you printed a PDF like this on U.S. Letter, you'd have to scale it a bit, which might make graphics and other things look a little funny or less clear.
A good option for doing something like this is to call around to local print shops near you and ask for a quote. If you live near a university, there should be a print shop in the vicinity of the university that's used to doing things like this. Specify number of pages, page size, paper weight, number of pages with color graphics, that you want spiral binding (make sure you want spiral not comb), and any options about covers. It's typical to use a transparent plastic cover for the front, make the first page a nice title page, and put an opaque plastic cover for the back.
They might ask you to send over the PDF before quoting a price. This would let them see how graphics heavy the manual is, basically how much color ink they'd have to spill.
If the user manual PDF doesn't incorporate the info from the datasheet, it might be a good idea to combine the two.
EDIT: If you have a friend with a color laser printer, you might be able to work out a deal with your friend for them to print the PDFs, then take the pages to a print shop for binding.