Combining PDFs
Today I was sent a license agreement as a 6 page pdf file, I was asked to sign the document and send it back. All very well but I was in a hurry and wanted to get to work a little faster than the postal service might allow. I have a scanner so I figured I could sign a copy of the last page then scan it and convert to pdf. I could have then sent the original license pdf plus the last page by email but that did seem a little unprofessional.
So then how to combine the signed page with the rest of the pages of the license agreement?
Well opening the original pdf in Preview I could select pages 1 to 5 to print and then use the "Save as pdf" option from the "PDF" button so create a new pdf with just the first 5 pages.

Now create an Automator workflow to join the files.
Open Automator and you should see a three pane window. The first pane contains the library of applications that have automator actions, the next pane shows the actions available for the selected application. Double click on an action to add it to the workflow in the third pane. No add these actions
From the Finder library select:-
Get Specified Finder Items
Sort Finder Items (and from the pulldown menus select "name" and "ascending"
From the PDF library select:-
Combine PDF Pages
Then finally from the Preview Library selct:-
Open Images in Preview.

Now save the workflow as Combine_PDF in "username/Library/Workflows/Applications/Finder/"
Now when you select several pdf files in the Finder, control-click (or right click) will bring up a menu that includes automator actions, choose combine_PDF and Preview will open showing a single document containing all files.

Note I added a sort option, this was to give some control over how the files were combined. If you now name them alphabetically then they will be combined as desired.




Comments
An existing app covers this
Automator is very slick. Alternately, here's a convenient Freeware app that can do the above, combining PDFs in different ways: PDFLab.
http://www.iconus.ch/fabien/pdflab/
-Ken
Two Sided Scanning
Great Post!! This could also be used in the event that you have a scanner and want to scan a two sided document, than you can scan the odd pages first (using the scanner's feeder) then scan the even pages, then combine them by changing the option in step 3 from "Appending Pages" to "shuffling pages".
Helpful Tutorial
I have do this about once a month or so. Last month I had to do this with png files. I had taken various snapshots of a pdb in pymol and I wanted to combine them into one pdf document in order to email. I ended up converting the png files in Fireworks to pdf then running automator.
Thanks for the PDFLab link. The app does exactly what I needed.
If anyone finds an automator app to convert images to pdf, please let us know.
Kit
Two Sided Scanning
What a good idea, I never thought of that.
Nice but...
well, you could do a lot better with what's freely available already.
I have been using the completely free (i.e. source too) "Combine PDF" for years now
versiontracker link: http://www.versiontracker.com/dyn/moreinfo/macosx/20286
it allows to reaarrange pages, add, remove, view individual pages etc.
Of course this would free up hours of debugging to dedicate to your research too :-D
a LaTeX solution
This is all great stuff.
I've been using LaTeX to patch together PDFs with the excellent and free TeXShop. It works a treat and is very flexible.
Here's how you could do the above in LaTeX. Paste the following text into a TeXShop document and click the Typeset button to makes the PDF file.
\documentclass[a4paper]{article}
\usepackage{pdfpages}
\begin{document}
\includepdf[pages=1-5]{original_file.pdf}
\includepdf[pages=1-1]{scanned_page.pdf}
\end{document}
You can get fancier by using the hyperref package to add metadata to your PDF. You can also type \includepdf[landscape, pages=1-] to include a PDF file in landscape mode.
file size comparison
First of all -- thanks for this work flow, which has really saved me a lot of time and effort. I did experience some odd side-effects, though. I attached 7 pdf files, 192KB in total, before and after a single large (5.9M) pdf file. The combined document's size was 8.7M.
On the other hand, using Jon Sullivan's method, the combined file remained 5.9M in size.