It’s very easy to merge 2 pdf documents or move single pdf pages from 1 pdf document into another with Big Sur. It’s built into the free Apple PDF reader called ‘Preview’. There are some small bugs in the interface, but it works. Here’s how to merge pdf documents in macOS Big Sur.

How to merge 2 pdf files.

Here’s how to merge 2 complete pdf files together.
e.g. You want to join a 10 page pdf file onto the end of a 15 page pdf file.

1. Open the first pdf file by double clicking on it. It should open into the Apple ‘Preview’ App.
2. If you want to keep a copy of your original unmodified document, select ‘Duplicate’ from the file menu so that you are now working on a new copy of the original file. Otherwise the new pdf file will be added to the original pdf file.
3. Make sure you can see the ‘thumbnails’ of the pdf pages on the left side of the window. If you can’t see the thumbnails, select ‘Thumbnails’ from the view menu to show them.
   

4. Find the second pdf file in the finder. It may be on your desktop, or in a folder.

5. Drag the icon of the second pdf file into the thumbnails of the first document. The place where you drop it will be the place the document is inserted.

e.g. If you drop it after page 1, the entire pdf will be places after page 1. (See the picture below).

6. Save your new merged pdf document (File menu – save or Press Command -S).

How to move pages between pdf files.

You can move individual pages from one pdf document into another. To do this, follow the steps above, but open both pdf documents so that you have both documents side by side, with the thumbnails in view. Now you can drag the individual pages from the second pdf file into the first one.

You can drag any number of pages from any number of pdf files, rearrange them, and then save the original file and it will include all the extra pages in the order that you set. You can even rearrange the order of the pages in the original pdf file. If you want to delete a page, just select the page in thumbnail view and press delete.

Some bugs

There are some problems with the interface in Big Sur. It won’t affect you pdf document, but it may confuse you.

1. Random Green Plus sign

Sometimes a little green ‘plus’ sign appears, but sometimes it doesn’t. Sometimes it stays permanently until you drop the page into the file, sometimes is disappears after a half a second. Don’t worry. This doesn’t change the outcome at all. It used to be that in older versions of macOS the files only merged if the plus sign was there but I can confirm this is not the case with Big Sur. The pages merge irrespective of the presence of the plus sign. So you can completely ignore the plus sign.

2. Number of pages in the new pdf

At the top of a pdf document there’s a line that says ‘Page 1 of 2.’ This lets you know how many pages in the pdf file. Once you have added a new page to the pdf document, this page counter can be slow to update. So you may have dropped a 3rd page into a pdf file but the counter still says Page 1 of 2. Don’t worry. You can completely ignore this counter. It seems to be a bug. I hope it gets fixed soon. If you click into the thumbnails is should update. But if you just click onto the original document it doesn’t update. To be sure, just close the original document then open it again and the page count should have updated.

If this gets fixed by Apple I’d love it if someone could leave a comment below!