Icecream PDF Split and Merge is a free tool for splitting PDFs, merging them, or just removing pages that you don't really need.
Surprisingly, the Split module can only handle one file at a time. But you do at least get plenty of control, with options to split your file into single pages, groups (sets of x consecutive pages starting from page y) and ranges (any specified range, like 3-9 or 12-14), while you're also able to delete any specified page numbers.
There's also some flexibility over the destination, with options to save your split files into a subfolder, the source folder, or some other folder of your choice.
Click Split when you're done and the program splits your source file almost instantly, then offers to open the folder for you to view the results.
The Merge module is more straightforward: drag and drop your source files, rearrange them into the preferred order, choose a destination folder and merge them with a click.
There is one notable plus, though: both the Split and Merge functions will work with encrypted files, as long as you know and enter the password.