To join two or more pdf files together using Preview (the standard pdf viewer in OS X) simply open a pdf in preview, open the thumbnail view (Shift-⌘-D), and then drag a second pdf file ON TOP OF an existing page thumbnail. The two documents will merge into one. Then save the new combined file. Read on for step-by-step instructions.
Combining pdf documents in OSX is easy. Leopard and Snow Leopard have the ability to move pdf pages around and even merge two pdf documents together. It’s built right in to OS X – you don’t need a third party program to do it!
SUMMARY: To merge the two PDF files you need to drag the new pdf ON TOP OF an existing 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. See these two pictures below to visualise the difference.
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