How to combine multiple PDF files into one

If you have several PDF files, scans or image files that you wish to combine into a single PDF file, whether the files are JPGs or PDFs, you can accomplish this using the Preview application, which is part of Mac OS X. If combining multiple single-page PDFs is your goal, follow the steps under "Directions A" below. However, a common need is to replace the final (signature) page of a multi-page PDF document with a newly scanned and signed version of that page. This can also be accomplished using the Preview application, but involves a couple of extra steps. For this procedure, follow the steps under "Directions B" below.

Directions A (Combining multiple single-page PDF documents into a single multi-page PDF document)

1. Select the PDF files in the Finder and drag them all together onto the Preview application's icon (which should be in the dock or, if not, drag them into the Preview application in the Applications folder).
2. In the Preview application make sure you are viewing the documents in "Thumbnails" view - if necessary, click the Thumbnails button up on the top right of the Preview window. (You may find it easier to use the "Contact Sheet" view by clicking on the Contact Sheet button instead.)
3. Drag the thumbnails up and down (if in Thumbnails view) until they are in the right order. (*If any pages are upside down, see Note A below.)
4. Select All the thumbnails by clicking on them with the shift key or from the Edit menu.
5. Choose Print in the File menu.
6. In the lower left of the Print dialog choose PDF->Save as PDF.
7. Name the combined PDF file and save it.

Note A: If when you check the resulting PDF file any individual pages are upside down, then from the Tools menu choose Rotate Right twice for each page before proceeding to step 4.

Directions B (Replacing a single page of a multi-page PDF document with a newly scanned single-page PDF document)

1. Select the multi-page PDF document in the Finder and open it in the Preview application (by dragging it onto the Preview application's icon, which should be in the dock or, if not, by dragging it onto the Preview application shown in the Applications folder).
2. In the Preview application make sure you are viewing the document in "Thumbnails" view - if necessary, click the Thumbnails button up on the top right of the Preview window. (You may find it easier to use the "Contact Sheet" view by clicking on the Contact Sheet button instead.)
3. Some multi-page PDF documents do not permit you to delete an individual page. To determine if this is the case, click on the thumbnail for the page you wish to delete; then see if the Delete command is available in the Edit menu. If it is, skip to step 6.
4. If the Delete command is not available in the Edit menu, you'll need to make a duplicate (unprotected) copy of the multi-page PDF document before you can delete the desired page. Make a duplicate using the Duplicate command in the File menu, then close and discard the original.
5. Select the thumbnail for the page you wish to delete. You should now be able to continue with the next step.
6. Choose the Delete command in the Edit menu. You should now see thumbnails for all but the deleted page.
7. Rearrange your windows as necessary so that you can see the replacement page in the Finder's Desktop as well as the Preview window's Thumbnails column.
8. Drag the replacement page into Preview's Thumbnails column.
9. Drag the thumbnails up and down (if in Thumbnails view) until they are in the right order. (*If any pages are upside down, see Note B below.)
10. Select All the thumbnails by clicking on them with the shift key or from the Edit menu.
11. Choose Print in the File menu.
12. In the Print dialog choose PDF->Save as PDF ... in the lower left.
13. Name the combined PDF file and save it.

Note B: If when you check the resulting PDF file any page is upside down, then either rescan the page or from the Tools menu choose Rotate Right twice before proceeding to step 10.