Reader Jamie Stone is perplexed by a Preview behavior changed in Snow Leopard. He writes:
Since upgrading to Snow Leopard, I can no longer combine PDFs like I could in Leopard with Preview. Any suggestions?
You can still combine PDFs, it just works a bit differently than it once did.
Under Leopard, you drag thumbnails from a PDF document open in Preview into the sidebar of another PDF document. A red line appears beneath the page thumbnail of the file you’re dragging to, indicating where the dragged page will be inserted. Save the file and you’re done.
Snow Leopard works a bit differently in that if you drag thumbnails from one PDF window to another, place them below the other document’s thumbnails, and save, you wind up with a document that contains just the pages you dragged into the sidebar.
The trick is to drag thumbnails on top of a thumbnail in the document you’re dragging to. This combines the pages. If you want to rearrange the pages, just drag them where you like–they’ll stay within the combined document. Save your document and you’re done.
If you’ve opened two PDF files at the same time and therefore find both documents in the sidebar, the technique is similar. Expand the document you want to move pages from by clicking the left-pointing arrow and drag the pages you want to copy on top of the icon of the other document in the sidebar. Reposition as you like. When you’re done, choose Save All from the File menu.