It's still there:
Mac OS X v10.6: How to combine PDF documents using Preview: http://support.apple.com/kb/HT4075
Drag the thumbnail of one PDF document (source) over of the thumbnail of the other PDF document (destination) and release the mouse or trackpad button when the pointer shows a green circle with a plus symbol in it. This will copy all pages from the source PDF and add them to the end of the destination PDF.
hm. No green circle appears, and I waited at least fifteen seconds...
My version of Preview (though it's dated 2012) seems out of date — it looks different from what I see here: http://support.apple.com/kb/HT4075. But I can't find where to download a new version of Preview.
This functionality is still available. The only condition is that all documents that are being merged should be in pdf format. Even if one of them is not, the merging capability is removed. Documents in jpeg and some other formats open by default in Preview. These can be exported to pdfs through File -> Export -> PDF before trying to merge.
Okay, finally figured it out for the latest version of Preview. Open the document you want on top, in Preview. Then expand the sidebar and change it to thumbnails. Then open Finder so that it overlaps the Preview window as little as possible, navigate to your file, then drag and drop the icon into the sidebar.
It actually does work in Mavericks, just as it did before. Here is the trick:
1) View thumnails of first file in Preview.
2) Drag icon of next file ABOVE NOT BELOW the faint horizontal line after the last page of the first document.
3) Continue with additional files.
Now, the additional pdfs will be incorporated into the original file.
How it works for you all.
None of the above methods worked for me :(.
For now, this seems to work:
1) In FINDER, double click the 1st file to be merged.
2) in PREVIEW, click Edit/ Insert/ Page from File.
3) Select file in popped up menu/FINDER. Keep doing 3) until no more file to merge.
4) Click File/Save.
Similar Acrobat, except can't choose where in the file to merge.
It looks like Preview (at least the version of Mavericks) doesn't handle PDF vs image files (eg. JPG) the same way when combining.
The drag and drop tip over or just above the thumbnail of the first file works fine for me when dealing with PDF files. The insert file method also when it is PDF files.
None of these methods are working for me when dealing with JPG files for instance.
I found that if I:
1. Show edit toobar - which is in View or is a button next to the search bar in Preview
This causes a small addition symbol "+" to appear in the bottom left corner of the icon menu on the left side of preview.
2. Click on the addition symbol and you'll be given three options
Insert page from scanner
Insert page from file
Insert blank page
3. Once I inserted from file (I already had the pdf) I could then save it as a single document.
The above methods always kept the documents separate and did not allow me to merge.