How the merge works
Each PDF is opened in your browser with pdf-lib, an open-source PDF library. Its pages are copied, in the order shown in the list, into a brand new PDF, which is then saved to your device. The page count shown for each file is read the same way, before you merge.
Pages in merged file = pages in file 1 + pages in file 2 + … + pages in the last file
Worked example: a rental application packet
A landlord asks for one PDF. You have a 2-page signed application, a 3-page bank statement and a 1-page photo ID scan. Add them in that order: 2 + 3 + 1 = 6 pages. The merged file keeps each page at its original size, so a Letter application and an A4 statement sit side by side without being stretched.
Where your files go
Nowhere. The page downloads its code once, then all the work happens on your device. There is no upload step, no account and no copy kept on a server. That matters for the documents people most often merge: pay stubs, tax forms, leases, medical records and ID scans. You can check this yourself by loading the page, turning off Wi-Fi, and merging.
Common uses
- Renter and loan applications. One file with the application, pay stubs, bank statements and ID, in the order the agent asked for.
- School and job forms. Combine a filled-in form with transcripts, a resume or a scanned signature page before uploading to a portal that accepts only one file.
- Receipts and invoices. Put a month of receipts into one PDF for an expense report or your accountant.
Limits to know about
| What | What happens |
|---|---|
| Password-protected or edit-locked PDFs | Refused, with the file named. pdf-lib cannot decrypt files, and copying encrypted pages would give blank pages. |
| Fillable form fields | May stop being fillable. Fill the form and print it to PDF first. |
| Bookmarks (outline) | Not carried over. |
| Page size and rotation | Kept exactly as in each source file. |
| Very large files | Limited by your device memory, not by the tool. |
To unlock a PDF you are allowed to open, print it to a new PDF: on Windows choose "Microsoft Print to PDF", on a Mac choose PDF, then "Save as PDF" in the print dialog, and in Chrome choose "Save as PDF" as the printer.
Questions people ask
Are my PDFs uploaded anywhere?
No. The merge runs in your browser using JavaScript. The files are read from your disk into the page, combined, and saved back to your Downloads folder. Nothing is sent to a server, and the tool keeps working if you disconnect from the internet after the page has loaded.
Why does it say my PDF is encrypted?
The file has an encryption dictionary. That covers PDFs that ask for a password and also ones that open freely but are locked against editing or printing, which banks, payroll systems and e-signing services often produce. This tool cannot decrypt them, and copying their pages without decrypting would give blank pages, so it refuses them. Open the file, choose Print, pick "Save as PDF" or "Microsoft Print to PDF", and add the new copy.
Is there a limit on file size or page count?
There is no fixed limit. The practical limit is your device memory, because every file is held in memory while it is merged. A few hundred pages of ordinary documents is fine on a laptop. Phones have less memory, so very large scanned files are the ones most likely to fail there.
Will links, bookmarks and form fields survive?
Page content, images, text and page rotation are copied exactly, and links on the page usually still work. The bookmarks outline is not carried over, and fillable form fields can stop being fillable, so fill in a form and print it to a new PDF before merging if you need the answers kept.
Can I merge PDFs on an iPhone or Android phone?
Yes. Tap the drop area, choose files from Files or Google Drive, put them in order with the Up and Down buttons, and tap Merge. The merged PDF goes to your Downloads (Files app on iPhone).