What the PDF merger does
Merge PDF combines two or more PDF files into a single document, in the order you add them. The pages are copied exactly as they are — text stays selectable, links keep working, vector graphics stay sharp — because the tool moves page objects between documents rather than re-rendering anything. Everything happens inside your browser: the files are read into memory, combined with the pdf-lib library, and the result is offered as a download. Nothing is uploaded, which matters when the documents are contracts, bank statements or medical records.
How to use it
- Select the PDFs with the file picker. You can pick several at once; hold Ctrl (Windows) or Cmd (Mac) to multi-select.
- The files are combined in the order they appear in the picker, which is usually alphabetical by filename. To control the order, rename files with a numeric prefix (
01-cover.pdf,02-body.pdf) before selecting them. - Click merge, then download. The output is named
merged.pdf; rename it after saving.
What is preserved and what is not
| Feature | Preserved? | Notes |
|---|---|---|
| Page content (text, images, vectors) | Yes | Copied byte-for-byte |
| Page size and orientation | Yes | Mixed sizes are allowed in one file |
| Internal links within a page | Yes | |
| Fonts | Yes | Embedded fonts travel with their pages |
| Bookmarks / outline | No | Outlines are document-level and are not merged |
| Form fields | Partial | Fields copy, but duplicate field names across files can conflict |
| Document metadata (title, author) | First file only | Edit afterwards with the metadata tool |
| Password protection | No | Encrypted files must be unlocked first |
Why file size may not add up
Merging three 1 MB files does not always produce a 3 MB result. If the files share the same embedded fonts, each copy is included separately, so the merged file can be slightly larger than the sum. Conversely, pdf-lib writes a clean, compacted file structure, so PDFs that carried leftover data from many edits can shrink. If the merged file is too large to email, run it through the compress tool afterwards.
Common uses
- Applications and submissions — combine a cover letter, CV and certificates into the single file a portal requires.
- Scanned documents — phone scanner apps often produce one PDF per page; merge them into one document.
- Reports — append an appendix or a signed signature page exported from a different program.
- Invoices and receipts — bundle a month of receipts for an expense claim.
- Print jobs — send one file to a print shop instead of a folder of parts.
Limits and troubleshooting
- Large files. Because the work happens in browser memory, very large merges (several hundred megabytes) may fail on phones or low-memory machines. Desktop browsers handle files of 100 MB or more comfortably.
- Encrypted PDFs. A file that asks for a password when opened cannot be merged until it is unlocked. Use the Unlock PDF tool first — you need to know the password.
- Corrupt files. PDFs produced by unusual generators occasionally fail to parse. Opening and re-saving the file in a viewer (Preview, Chrome, Acrobat) usually repairs it.
- Wrong order. If the output order is not what you wanted, use the Reorder Pages tool on the merged file, or rename the inputs and merge again.