If you need to merge couple (or more) different PDF documents into one, pdfresizer.com is a great online tool that can do it (and some other PDF manipulations) perfectly. I prefer this particular site because there are no watermarks and sane file size limits.
- Head over to https://pdfresizer.com/merge
- Click the “Browse” button and select all the files you want to merge
Use Ctrl+click to select all the files you want to use
- Re-arrange the files in your preferred order.
Drag’n’drop the files in your preferred order
- Click the Magic button and save the resulted file to your computer.
pdfresizer.com also offers bunch of other tools for PDF splitting, resizing and optimizing, they all work in a similar fashion.