This article recommends two ways to combine & join PDF files.
To combine two PDF files together using Preview (the standard PDF viewer in all Mac OS X):
1. Simply open the PDF file in preview.
2. Open the thumbnail view (Shift-Command-D).
3. Drag a second pdf file ON TOP OF the existing page thumbnail.
NOTE: The second opened PDF file must be on top of the first opened thumbnail. If you drag it into the sidebar but not on top of an existing page the new file will be added as an external link – not merged into the original pdf document.
1. Open the PDF documents that you want to combine in Preview.
2. Show the sidebar in each Preview window. If the sidebar is not showing, click the Sidebar button in the Preview window's toolbar, or choose View > Sidebar > Show Sidebar.
3. Verify that the sidebar is configured to show thumbnails (this the default view). If the sidebar is not showing thumbnails, choose View > Sidebar > Thumbnails.
4. Drag the thumbnail of one PDF document (source) over of the thumbnail of the other PDF document (destination) and release the mouse or trackpad button when the pointer shows a green circle with a plus symbol in it. This will copy all pages from the source PDF and add them to the end of the destination PDF.
5. If the pages in the destination PDF are shown in the wrong order, click the gray circle containing an arrow that appears over the PDF document's thumbnail, so that the arrow points to the right, and drag the thumbnails of the individual pages into the desired order.
6. After the destination PDF contains all of the pages you want and the pages are in the correct order, you can select File > Save As to save a new PDF document containing all of the combined pages, or you can select File > Save to replace the original version of the destination PDF with the version containing the combined pages.
If you want to combine & join pages or multiple PDF files together on Windows, you can use PDFMate Free PDF Merger to help you out. This Free PDF Merger is an easy but powerful program for merging multiple PDF files into a single one. It also converts images to PDF files, split PDF pages, and encrypt PDF with new password for protection.