Here’s the original method I outlined…
1. Open the two pdf files in Preview.
Double click on the two pdf files to open them in Preview.
2. Turn on ‘Thumbnails’ for both documents.
There should be an icon in the top left of the preview window where you can turn on ‘Thumbnails’. (See picture below.) This will open a sidebar on the left where you can see a thumbnail picture of each page in the pdf file.
3. Drag a thumbnail to merge it – but read the fine print below!
To combine a page from one pdf into the other pdf file you drag the thumbnail from one of the preview windows onto the thumbnail pane of the other preview window. In my example I need to click and then drag one page from 2.pdf to 1.pdf to add my second document to my first.
VERY IMPORTANT: Exactly where you drag the pdf thumbnail to, will change what happens. Do it slowly and don’t release the mouse click until you see what will happen. Here’s how it works.
(A) If you drop the copied thumbnail inside the destination thumbnail, a little green plus will appear, and you’ll get a double grey border. This means the new pdf will be merged into the first pdf.
Here’s what this looks like:
(B) If you drop the thumbnail a little bit underneath (south) or above (north) of the destination thumbnail, no green plus will appear, and you’ll get a single grey border. This means the new pdf will not be merged into the first pdf.
If you want to merge the entire document then you need to select and drag all the pages across.
4. Confirm it worked.
Look at the title in the pdf window. It should indicate 1 document with 2 pages like this:
5. Now you can just choose ‘Save’ and the merged file will be saved.
6. If it looks like this second title (below) with ‘2 documents’ in the title, this indicates that it didn’t merge. You may have done something wrong.
You are just viewing 2 documents in the same window. Don’t worry, all is not lost. You can now choose ‘print’ to print both these documents at once, then click on on ‘Save as PDF’ to print these two documents into one pdf file.