With every release of OS X Apple seems to slightly change the way to merge two pdf documents. I’ve previously written on how to merge 2 pdf files in Mountain Lion (10.8) and how to merge two pdf files in Lion or earlier. Here’s how to do it in OS X 10.9 Mavericks.
John has just posted a much easier method of doing this in a comment below. Thanks John, here it is:
1. Double click your first pdf document to open it with Preview, the built in mac OSX.
2. Go to the “Edit” drop down menu, find “Insert” and then “Page from File…”
3. Click on the file (or files) that you wish to import.
You can delete pages by selecting the page in the page thumbnails and pressing delete.
You can rearrange pages by selecting the page in the page thumbnails and dragging it up or down.
Whatever changes you make will be saved when you select ‘Save’
Make sure all files are pdf files…if you’re using .doc files, save them as pdf first.