How to combine PDF files into one, and where it goes wrong
Where merging several PDFs into one gets stuck on Windows, Mac and iPhone. And what to fix when the merged file comes out in the wrong order, with blank pages, or too big to send.
Merging is simple in principle: the first page of the next file goes after the last page of the one before. People get stuck in two places. Finding something that will do it, and opening the result.
Windows has no Merge option, and Acrobat Reader will not do it either
Select several PDFs in File Explorer and right-click: there is no Merge or Combine. The usual next idea is to print them all to "Microsoft Print to PDF" and hope they land in one file. A question on Microsoft Q&A from June 2021, which more than 20 people marked as having the same problem, describes what actually happens:
The Print option in Explorer doesn't merge the files, it merely prints them to PDF separately. I don't see a print dialogue, only a save file dialogue once I click on print, and there's a separate save file dialogue for each file I selected.
From the question "Can't Merge multiple PDF files into one file in Explorer".
The asker was confused for a good reason. Online guides promised the trick would work, and it had worked for them with images. With PDFs it produces one file per PDF. An answer to a different question on the same site (2020) puts it bluntly: "Windows and Office do not ship with tools that can merge PDFs."
Having Acrobat Reader installed does not change that. Adobe describes Reader as the app for people who "primarily need to view, print, and lightly annotate PDFs". When someone on the Adobe Community forum asked why they could no longer combine files in Reader (4,783 views), the reply was that "Reader has never been able to combine files although you can get a subscription that is accessible through Reader to combine files online." What Adobe offers for free is its Merge PDF page on the web: up to 100 files, 500 pages per file and 1,500 pages in the result. Adobe says the files are handled on its servers and deleted unless you sign in to save them.
That leaves three routes on Windows: install a free program, upload to a website, or use a tool that runs inside the browser. Plenty of people rule out the first two before they start. From a Windows 11 forum in 2025:
a.) I don't want to pay an Adobe subscription and also have to download their bloatware. b.) And because there's confidential information on existing pdfs, I don't want to upload them to any free website, either.
From the thread "How can I merge pdfs?", February 2025.
The replies suggested installable tools such as PDFsam and LibreOffice. If you are allowed to install software, those are reasonable choices. If you are not, a browser tool that keeps the files on your machine is what remains.
Mac and iPhone can do it, with a couple of traps
On a Mac, Preview does it. Apple's guide: open the PDFs, choose View > Thumbnails in each window, then drag the thumbnails you want from the sidebar of one PDF to the sidebar of the other. You can drop them at the end or between pages.
The trap is in the same guide: "Changes you make to a Preview document are saved automatically." Drag an appendix into the contract you were sent and the contract file itself has changed. If the original needs to survive, use File > Duplicate first and work on the copy.
The Finder is quicker. Select the files, Control-click, and choose Quick Actions > Create PDF. Apple notes: "The files appear in the PDF in the same order that you select them." That means click order, not name order. If order matters, Command-click the files one at a time, starting with the first.
On iPhone and iPad, the Files app can do it, though we could not find the steps in Apple's own user guide. An answer on Apple Support Communities gives them: tap the three-dot button at the top right, tap Select, pick the PDFs, then tap the three-dot button at the bottom right and choose Create PDF. The person who posted it explained why people miss it:
What messed me up the first time I tried the instructions is that there are two different icons with three dots. The first one you use is at the top right. The second one is at the bottom right.
Reply in the thread "Merging documents feature on iPad IOS18 missing", February 2025.
The pages came out in the wrong order
When you hand a program several files at once, the program decides the order. Some use the name, some use the order you clicked, some use whatever order the files arrived in.
| How you merged | What decides the order |
|---|---|
| Mac Finder, Quick Actions > Create PDF | The order you selected the files (Apple's guide) |
| A program that sorts names as plain text | 1, 10, 11, 2, 3 |
| A program that reads the numbers in names | 1, 2, 3 … 10, 11 |
Numbering files 01, 02, 03 instead of 1, 2, 3 gives the same order under every kind of sort. Worth doing once you have more than nine files.
If you only notice after merging, you do not need to start again. Move the pages instead. A stack that went through a document feeder the wrong way round, with page 1 now last, only needs its order reversed.
A password-protected PDF in the pile
Bank statements and payslips sent by email sometimes ask for a password when you open them. Their contents are encrypted, so a program that does not have the password can copy the pages but cannot read what is on them. Depending on the tool, you either get an error, or the merge finishes and that file's pages come out blank.
The merge tool on this site now stops a locked file as soon as you add it: the file is flagged in the list, a message says it is password-protected and the password has to be removed first, and it is not merged. Until we fixed this on September 30, 2026, it let such a file through and its pages came out blank. So unlock first, save the unlocked copy, and merge that. If you know the password it asks for when opening, Remove PDF password clears it. A file that opens freely but blocks printing or editing needs the password that set those restrictions; if you do not have it, asking the sender for an unrestricted copy is quicker.
The merged file is too big, or the pages are different sizes
Merging copies pages; it does not shrink them. Our test merged a 3.6MB and a 1.8MB PDF into a 5.4MB file. Gmail allows 25MB of attachments on personal accounts and, above that, removes the attachment and puts a Google Drive link in its place. Work and school accounts get whatever limit the administrator set. If the total is close to the limit, compress the heaviest file (usually a scan) before merging.
Page sizes are copied too. Merge an A4 document with a US Letter one and both sizes stay in the file. Photos cause the more striking version of this. In this site's Images to PDF tool, "Match image size" turns each pixel into a point, so a 12-megapixel phone photo (3024×4032) becomes a page 42 inches wide and 56 inches tall. Put that next to Letter pages and, with the viewer fitted to width, the Letter pages look about a fifth of the size. If photos are going into a document, make the PDF with "Fit to A4" instead.
Merging in the browser: what this site's tool does and does not do
Merge PDF joins the files inside your browser. Nothing is uploaded and nothing is installed. Drop in several at once and each shows its page count and size, with the combined size at the top. The tool does not re-sort by file name, so check the list and drag the handles to fix the order (from the keyboard: Space on a handle, then the arrow keys). You name the result, and it is saved as a new file, so the originals are untouched.
To fix the order after merging, Reorder PDF pages lets you drag pages or reverse the whole document in one click. Its thumbnails stop at 120 pages, so pages beyond that cannot be dragged.
What it cannot do: it does not compress while merging. It cannot interleave two files page by page (page 1 of A, page 1 of B, page 2 of A), which is what you would need to combine separately scanned fronts and backs. And bookmarks, the clickable outline some PDFs carry in the sidebar, are not carried over into the merged file. If you depend on the outline of a textbook or a long report, open the result and check it before you send it, whichever tool you used.
Common questions
- Does merging reduce quality?
- No. Pages are copied as they are, not redrawn, so text and images match the originals.
- Can I merge photos and PDFs together?
- Merge PDF only accepts PDFs. Turn the photos (JPG, PNG or iPhone HEIC) into a PDF with Images to PDF first, then merge.
- The Merge button stays greyed out.
- It needs at least two readable PDFs. A file marked "Not readable as a PDF" does not count.
- I need to drop a few pages from the merged file.
- No need to merge again. Remove them with Delete PDF pages.
- Does it work on a phone?
- Yes. If the files add up to more than 40MB on a phone, a notice warns that the browser may run out of memory, and a computer is the safer choice.
Last updated September 30, 2026 · As of September 30, 2026. Checked against Adobe's online Merge PDF page, Apple's Preview and macOS user guides, and Gmail's attachment help on that date. The behaviour of this site's merge tool (locked files, bookmarks, page sizes, file size) was tested with sample files on the same day.
