Split PDF
Extract page ranges or break a document into single pages.
Merge PDF
Combine PDFs and reorder pages by dragging. Nothing is uploaded.
What it does. Merging PDFs combines several documents into a single file with the pages in an order you choose. This tool does it inside your browser using pdf-lib, so contracts, invoices and medical records are never transmitted to a server. There is no page limit, no file size cap and no watermark.
Runs in your browserNothing uploadsNo signupWorks offline
How to use Merge PDF
- Drop two or more PDF files onto the panel. Page thumbnails render as each file loads.
- Drag the file cards to set the order, and remove any you did not mean to include.
- Click Merge, then download the combined PDF.
How does merging work without uploading anything?
A PDF is a structured binary document: a header, a body of numbered objects, a cross-reference table pointing at each object’s byte offset, and a trailer. Merging means copying the page objects and their dependencies — fonts, embedded images, color profiles — from each source document into a new one, then writing a fresh cross-reference table.
None of that requires a server. This tool reads each file with the File API, parses it with pdf-lib in a Web Worker, copies the page trees, and serializes a new document into a Blob that your browser offers as a download.
The reason mainstream services upload instead is not technical necessity. It is that a server-side pipeline is easier to monetize with page limits and subscriptions.
Why does this matter more for PDFs than other files?
Because of what people merge. Look at the actual use cases: combining a signed contract with its exhibits, assembling a mortgage application from bank statements, merging medical records for a specialist referral, putting together an immigration file, compiling invoices for an accountant.
Nearly all of it is personal or commercially sensitive. Uploading a set of bank statements to a free web service means trusting their retention policy, their access controls, their subprocessors and their breach history — for a task that is fundamentally just concatenating byte arrays.
For anyone handling EU or UK personal data, sending client documents to a third-party processor without a data processing agreement is a GDPR problem regardless of how quickly the files are deleted afterwards. Local processing removes the transfer, and with it the question.
What is preserved when files are merged?
| Element | Preserved | Notes |
|---|---|---|
| Page content and layout | Yes | Copied object-for-object |
| Embedded fonts | Yes | Carried across; duplicates are shared |
| Images and color profiles | Yes | Referenced, not re-encoded |
| Page size and orientation | Yes | Mixed sizes stay mixed |
| Internal links and bookmarks | Partly | Intra-document links survive; outlines may flatten |
| Form fields (AcroForm) | Partly | Fields are kept; duplicate names can collide |
| Digital signatures | No | Any signature is invalidated — this is by design |
| Annotations and comments | Yes | Copied with their pages |
The signature row is important and is not a limitation of this tool. A digital signature certifies the exact bytes of the document it was applied to. Any modification — including merging — necessarily breaks that certification. If you need a signed document inside a merged file, merge first and sign the result.
How large a file can it handle?
Your device’s available memory is the limit, not a server quota. In practice, merging documents totaling 200–500 MB works comfortably on a laptop with 8 GB of RAM, because pdf-lib streams object copies rather than holding every page rasterized.
For comparison, the free tiers of the major online merge services cap around 100 MB total and 20–25 files per operation, with hourly limits on top. Those caps exist to control their bandwidth and compute costs — costs that do not exist when the work happens on your machine.
Very large scanned documents — hundreds of pages at 300 DPI — are the one case that can strain a phone. On desktop it is rarely an issue.
Can I reorder pages, not just files?
Yes. Each file expands into its page thumbnails, and thumbnails can be dragged individually across the whole merge set. That lets you interleave documents — alternating pages from a double-sided scan done in two passes, for example, which is otherwise an awkward manual job.
Individual pages can also be rotated or deleted before merging, so a document that arrived sideways does not require a separate trip through a rotation tool.
Frequently asked questions
Is there a limit on how many PDFs I can merge?
No count limit. The practical constraint is device memory, which typically allows hundreds of files or thousands of pages in a single operation.
Does it add a watermark?
No. No watermark, no page cap, no signup, and no paid tier — there is no server cost to recover.
Will my file be deleted from your server?
It was never on a server. The file is read into your browser’s memory and discarded when you close the tab.
Can I merge password-protected PDFs?
You will need to supply the password. An encrypted PDF cannot be parsed without its decryption key. Owner-password restrictions that only prevent printing can generally be worked around; user-password encryption cannot.
Does merging reduce quality?
No. Page content is copied as-is, not re-encoded. The output pages are byte-equivalent to the source pages.
Why is my merged file so large?
Because it is the sum of its parts, plus shared resources deduplicated. If each source embeds the same font subset separately, the total can be smaller than the sum. Run the result through Compress PDF if size matters.
Can I merge a PDF with a Word document?
Not directly. Export the Word file to PDF first — every version of Word has Save As PDF — then merge the two PDFs.
Guides for Merge PDF
- Choosing Fonts for PDFs That Matter7 min read
- Choosing and Setting Your PDF Viewer6 min read
- PDFs on iPhone and iPad6 min read