How to Merge PDFs on Mac (Preview Sidebar Trick)

You don't need Acrobat or a sketchy "free PDF merger" website to combine PDF files. Preview — already on every Mac — merges documents by letting you drag pages between thumbnail sidebars. Here's the whole trick, plus how to reorder pages and save the result without wrecking your originals.

Merge two PDFs by dragging pages

1. Open both PDFs so each has its own Preview window.
2. In each window, choose View → Thumbnails. A sidebar of page thumbnails appears on the left.
3. In the source document's sidebar, click a page — or press Cmd+A to select every page.
4. Drag the selected thumbnails into the other window's sidebar. A blue insertion line shows exactly where the pages will land — between existing pages, at the start, or at the end.
5. Drop them. The pages are now part of the second document.

You can keep dragging pages from as many open PDFs as you like. Preview handles differing page sizes fine — each page keeps its own dimensions. This also works between a PDF and itself: drag a page's thumbnail within the same sidebar to move it, or Option-drag to duplicate it — useful for repeating a cover sheet or terms page.

Insert a whole PDF without a second window

If you just want to append an entire file, skip the window juggling:

1. Open the main PDF and show thumbnails (View → Thumbnails).
2. Click the thumbnail of the page you want the new content to follow.
3. Choose Edit → Insert → Page from File… and pick the second PDF.

Every page of the chosen file is inserted after the selected page. Edit → Insert → Blank Page lives in the same menu if you need a separator page.

Reorder pages and save it properly

Drag thumbnails up and down the sidebar to reorder pages at any time. To move several at once, Cmd-click each thumbnail first, then drag the group.

Saving is where people get burned:

• File → Export as PDF… writes a new merged file and leaves the document you were editing alone on disk until you close it. This is the safe route.
• File → Save (Cmd+S) writes the changes into the PDF you dragged pages into, overwriting it.

Made a mess? Cmd+Z undoes page moves before you save, and File → Revert To → Browse All Versions… can roll a saved file back to an earlier state. If a document refuses to accept pages at all, it's likely password-protected against editing — you'll need the owner password first.

No Preview at all: the Finder shortcut

For a quick "staple these together in order" job, you don't even have to open a window. Select the PDFs in Finder — Cmd-click them in the order you want them combined — then right-click and choose Quick Actions → Create PDF. Finder writes a single merged PDF into the same folder, originals untouched. You give up control over individual pages, but for expense receipts or scan bundles it's the fastest merge on the Mac.

Two caveats worth knowing with either method: page numbers printed on the pages obviously don't renumber themselves, and bookmarks or a table of contents from the source files don't carry into the merged copy. If navigation matters, add it back afterwards or keep the originals alongside.

One more tip: shrink the result

Merged PDFs can balloon in size, especially when scans are involved — combine three scanned agreements and you can easily cross the 25 MB email attachment ceiling. Preview's Quartz filter can compress the whole file on export, usually cutting scans down dramatically with little visible loss — see how to compress a PDF on Mac before you email the result.