Enter one of my new favorite free tools: FoxyUtils.
FoxyUtils is an online program that lets you merge, split, unlock and protect pdfs for free. It works on both PCs and Macs, which is a big help for those of us in the Apple world. If you sign up for a free account, you can merge files up to 50 MB; if you don't want to sign up, you can still merge files up to 30 MB.
If you need to combine even larger pdfs (up to 200 MB) and want to enjoy the benefit of viewing the site without ads, you can set up a paid account for $4.99 per month.
This program saved me endless time and hassle last week when I needed to combine several large pdfs into one file for a client's CreateSpace book. I haven't used the other options (unlock or protect) yet, but expect I will in the near future.
Have you used this resource? Got another favorite online freebie? Let me know!