Merging PDF Documents in Preview on Mac OS X Snow Leopard

Preview in Mac OS X is not only a viewer for PDF (and other) documents, it allows you to merge multiple PDF documents into one. This is useful for a lot of reasons, especially when you have scanned several pages of a documents into individual files and you want to combine them.

In Snow Leopard the way this works has changed and, as there is no menu item for merging, it can be a little confusing.

Open your first 'page' or document in Preview and open up the sidebar.

If you drag a new document into the sidebar and drop it in a blank region you will see that appear in the viewing window. But this has not added this page to the first. Preview is simply allowing you to view two separate documents.

To combine pages, drag and drop the second page on top of the first. The second page will appear as thumbnail in the sidebar below the first AND the two pages will appear in the same document in the main viewing window.

This is confusing as both scenarios look the same in the sidebar. You can see the true document structure in the sidebar by picking one of the pages and moving it slightly as though you were reordering it. All pages in the same document will become surrounded with a border and shaded background.

You can reorder pages within a document by dragging and dropping as needed and 'Save As' will save the merged document as a single file.

It is a great feature of Preview but the user interface means that it is effectively hidden unless you know about it.