When you are applying for a mortgage or assembling a massive report for work, you often end up with dozens of individual, single-page PDF files scattered across your desktop. Emailing twenty separate attachments to a client looks highly unprofessional and guarantees that at least one file will be lost in transit. You do not need to pay for an expensive Adobe Acrobat subscription to fix this. You can use the built-in macOS Preview application to effortlessly merge all of your loose PDF pages into a single, perfectly bound master document.
How to Enable the Thumbnails Sidebar
To merge documents in Preview, you must utilize the hidden “Thumbnails” interface, which allows you to physically drag and drop pages into the file.
- Locate your primary PDF file (the document that you want to serve as page 1). Double-click it to open it in Preview.
- Look at the top-left corner of the Preview window, right next to the window title. Click the Sidebar Menu button (it looks like a small square next to a vertical rectangle).
- From the drop-down menu, select Thumbnails.
A new sidebar will open on the left side of your screen, displaying a small visual preview of your current PDF page.
How to Merge Multiple PDFs Together
Now that the Thumbnails sidebar is active, merging documents takes only a few seconds.
- Minimize your web browser and ensure you can see both your open Preview window and your Mac Desktop (or Finder folder) containing the other loose PDF files you wish to merge.
- Click and hold one of the loose PDF files on your desktop.
- Drag the file directly over to the open Preview window, and hover it inside the grey Thumbnails sidebar (do not drop it on the main reading pane).
- A small green plus (+) icon will appear on your cursor, indicating that Preview is ready to ingest the file.
- Release your mouse button.
Preview will instantly rip the contents of the second PDF and append it to the bottom of the Thumbnails list. You can repeat this process as many times as you want, dragging fifty different PDF files into the sidebar to combine them.
Rearranging and Saving the Pages
Once you have dropped all your files into the sidebar, you can reorder them before finalizing the document. Simply click any page thumbnail and drag it up or down the list to change its page number.
If you accidentally dragged the wrong document into the mix, just click its thumbnail in the sidebar and press the Delete key on your keyboard to instantly remove it from the binder.
When the pages are perfectly ordered, press Command + S on your keyboard. Preview will permanently flatten the merged pages into a single, contiguous PDF file.