Split and merge PDF files. Free and open source - PDFsam
A powerful tool to visually Combine PDF files, Organize pages, Delete pages, Compress, Crop, Split when a given text area changes (Ex. invoice number), Split by pages, by bookmarks, by size, Rotate, Extract text, Repair, Convert to grayscale, Encrypt, Decrypt, Mix, Extract pages . Available for Windows, Mac and Linux. Try it free for 14 days.