I needed to be able to split some PDF documents for another site I’m working on, so I went searching on the internet for something I could use – preferably free, since I don’t think it’s something I’ll regularly need. I found PDFSam Basic (they also have a paid version), which did exactly what I needed. It can also merge PDFs, rotate them, and do a bunch of other things. If you need something free and easy to use, I highly recommend it!