Merge PDF

Combine multiple PDF files into one document. Reorder entire files or rearrange individual pages with drag & drop before merging. 100% in-browser — nothing is uploaded.

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Drop PDF files here or click to browse

Select 2 or more PDF files — No size limit

How to Merge PDF Files

Click the drop zone or drag and drop your PDF files
File Order mode: Drag file entries to reorder entire documents
Page Order mode: Switch to see every page as a thumbnail — drag individual pages to set a custom order across all files
Click Merge PDFs to combine them into one file
The merged PDF will download automatically

Why Merge PDFs?

Combine invoices — Bundle monthly invoices into a single quarterly or annual file
Create portfolios — Merge individual project PDFs into one portfolio document
Organize contracts — Combine multi-part agreements with appendices
Simplify sharing — Send one file instead of multiple attachments

Privacy & Security

Your PDF files are processed entirely in your browser using the pdf-lib JavaScript library. No files are uploaded to any server. You can verify this by checking your browser's Network tab.

How a PDF combiner actually works

Nothing is appended to your first file. A combiner creates a new, empty PDF and copies pages into it one source at a time, in the order you set. The originals are never modified — they are only read.

This matters because a PDF stores information in two different places. Some things belong to a page: its text, images, fonts, rotation and any link annotations sitting on it. Other things belong to the document as a whole: the bookmark outline, the interactive form definition, the title and author. Copying pages carries the first group across. The second group has nowhere to land in a document that was created empty a moment earlier.

That single distinction predicts everything a merge does, and it is why every browser-based combiner behaves the same way.

What survives the merge, and what doesn't

Kept — page content. Text stays selectable, images keep their original resolution, and fonts travel with the pages that use them. Nothing is re-rendered or re-compressed, so there is no quality loss at any point.
Kept — page size and orientation. Each page keeps its own dimensions. Merging A4 into US Letter produces one document containing both sizes rather than forcing everything onto a single page size — we verified 595×842 and 612×792 pages coexisting in one output.
Kept — rotation. A page recorded as rotated arrives rotated the same way.
Kept — links. Link annotations belong to their page and continue to work.
Lost — bookmarks. The outline sidebar is a document-level structure and is not carried over, from any of the source files. Merging ten bookmarked reports gives you one document with no outline at all.
Lost — form fields. Interactive fields are registered on the document, so after merging they stop being fillable and any entered values are gone. The printed boxes remain as static artwork.
Lost — document metadata. Title, author, subject and keywords all start empty, because the merged file is a genuinely new document rather than an extended copy of the first input.

File Order or Page Order?

File Order takes every page of each document in the sequence you arrange the files. It is the right choice for the common case — stitching whole reports, invoices or chapters together — and it is faster, because each source is copied in a single pass.

Page Order renders every page of every file as a thumbnail and lets you interleave them freely, which is what you want when assembling a document from scattered pages rather than whole files. The cost is that pages are copied individually, so resources shared between them can be written more than once. In our measurement the same fourteen pages came out about 2% larger in Page Order than in File Order — real, but small enough that you should choose the mode that matches the job rather than optimising for bytes.

Best practices when combining PDFs

Set the order before merging, not after. Reordering afterwards means a second rebuild, and every rebuild discards document-level structure again.
Merge last. If a document needs a bookmark outline or fillable fields, add them to the combined file, because the merge would have stripped them anyway.
Check the first page of each source. Mixed page sizes are preserved faithfully, which is usually what you want — but it does mean a stray Letter page inside an A4 report stays visibly different when printed.
Keep signed documents separate. A digital signature covers the exact bytes of the file it was applied to; rebuilding those pages into a new document invalidates it.
Combine in one pass rather than repeatedly. Merging A with B, then that result with C, costs an extra rebuild for no benefit — add all the files at once instead.

Limits

100 MB per file. Anything larger is skipped with a message rather than silently dropped. There is no cap on the number of files, but every file is held in memory while the merge runs.
At least two files are required before the merge button becomes active.
Empty or unreadable PDFs are skipped, and a damaged file reports which name failed so you can replace it.

Frequently Asked Questions

It builds a new, empty PDF and copies pages into it in the order you set, using pdf-lib entirely inside your browser. Your original files are only read, never altered. Because the output is a new document, anything stored per-page — text, images, fonts, rotation, links — comes across intact, while anything stored once for the whole document, such as bookmarks or form definitions, does not. No files are uploaded to any server.

Yes. All processing is 100% client-side. Your PDFs never leave your device or get transmitted over the internet. This makes it safe for confidential contracts, financial statements, and other sensitive files.

Yes. The tool preserves each page's original dimensions and orientation. You can freely combine portrait A4 pages with landscape letter-size pages — every page keeps its original formatting in the merged output.

Yes. After selecting your files, you can drag and drop them into any order before merging. The final PDF will follow the exact sequence you set, so you have full control over the page arrangement.

Each individual file must be 100 MB or smaller; larger ones are skipped with a message naming the file. There's no cap on how many files you add, but all of them are held in memory while the merge runs, so a few hundred pages is a more realistic ceiling on a modest device than the file count itself.

No — and this is true of browser-based PDF combiners generally, not just this one. Bookmarks and interactive form definitions are stored once for an entire document rather than on individual pages, so when pages are copied into a newly created file there is nothing to attach them to. Page content, images, rotation and links all survive untouched. If the combined document needs an outline or fillable fields, add them after merging.

The merged file is a genuinely new document, not an extended copy of your first input, so it starts with empty document properties rather than inheriting one file's metadata arbitrarily. Nothing inside the pages changes — only what a viewer shows in its document-properties panel. Set the title and author on the merged file if it matters.