Lifehacker: “Learn how to combine PDFs into one main file on both Windows and Mac devices. Combining multiple PDFs can be really stressful, mostly because the process isn’t clearly outlined in the programs you’re probably using to view the, and a lot of the third-party apps that offer the feature (like Adobe Acrobat) cost money. But if you want to combine PDFs together without paying anything extra, you can—you’ll just have to jump through a few hoops, depending on the type of computer you’re using…”