PDFsam works for merging scans of double sided documents

Occasionally I need to scan a double sided document. For a short documents (1-4) I just scan the fronts of the pages and then the backs and then manually put them together using Preview in Mac OS X.  However for longer documents the free PDF Split and Merge, or PDFsam, quickly merges these types of scans:

http://www.pdfsam.org/

How to create a Mac OS X keyboard shortcut to print to PDF

I was getting sick and tired of having to go to the mouse to click the PDF button from the Mac OS X print dialog every time I print a web page to PDF (which is really the only "printing" I do anymore). I googled around and found this awesome tutorial about how to set up a keyboard shortcut for this that I never would have figured out on my own in a million years:

Keyboard Shortcut for “Save as PDF…” in OS X at macsparky.com

This only gotcha I ran into is that you have to enter "Save as PDF..." with "as" in all lowercase in order for it to work. Entering "Save As PDF..." doesn't work.

Using Mac OS X Leopard Preview to Manipulate PDF Files

Update 2011-01-09: I finally got around to installing Snow Leopard on my main Macbook and discovered that Preview handles this stuff a little differently.  The instructions have been updated for Snow Leopard 

I do all my filing paperless, so I am in the habit of scanning batches of snail mail as a single PDF and then breaking out and saving pages as separate PDFs for filing, and sometimes combining multiple PDFs into a single PDF. In Windows I had always used Adobe Acrobat Professional to do this, but my personal Mac mini challenge was to replicate all the functionality I have in Windows in Max OS X Leopard.

I didn't see an obvious tool for this built-in to Leopard, so I spent a lot of time downloading and trying out various freeware applications (mostly Java based) for breaking apart and merging PDFs, but they are were all pretty awkward to work with. Then I decided to take a hard look at Preview to see if I could get it to do what I wanted. Here is what I found:

To extract a single pages of a PDF in Snow Leopard Preview:
1. Highlight the page(s) you want in the Sidebar and hit Command-C to copy to the clipboard (For some reason you can't seem to do this with multiple pages).
2. Then go File -> New from Clipboard (or just Command-N). A new Preview window opens up with just the single pages you copied.
3. Then do File -> Save As or Shift-Command-S to save the new PDF.
4. You can also drag the selected pages to the Desktop and it will create a new PDF of those pages.

To extract multiple pages of a PDF in Preview:
1. Extract a single page as outlined above.
2. Open your new single page PDF in Preview next to your already open source PDF.
3. Select all of the pages you want to extract in the Sidebar of your source PDF, and then drag and drop and drop them where you want them to go in the Sidebar of your target PDF. They show up in your target PDF where you dropped them.
4. Save your target PDF using File -> Save As or Shift-Command-S.

To combine multiple PDFs in Preview:
1. Open one PDF in Preview.
2. Drag the PDF file you want to add from Finder onto the Sidebar of the PDF you have open in Preview and drop it directly on top of the existing page (if it is a single page) or directly on top of the page with the binder showing (if the existing PDF is multiple pages).  In Snow Leopard, if you just drop the file on the sidebar it doesn't combine the PDFs by default; you have to drop directly onto a page.