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Combining several PDFs into one file

The reasons people merge PDFs are usually about delivery. A grant application has a section from each co-author and the funder wants one document. A travel packet has a flight confirmation, a hotel booking, and an insurance certificate, and you want one PDF on your phone for offline reading. A tax filing has the form itself plus several supporting documents, all of which need to arrive together. A contract body and its appendix were sent separately; the signer wants one packet to review.

The result is a single PDF that opens like any other. The pages flow from one source's content into the next in the order you arranged them. The original files stay untouched on your computer.

Putting the files in the right order

Drop your PDFs in. Each becomes a card with a thumbnail. Drag the cards to rearrange them — the order on screen is the order of the pages in the final document. Drop additional files at any point and they'll be added to the end, ready to be dragged into position.

Merge here works at the file level: each PDF you drop in contributes all of its pages, in their original order. If you only want some pages from a particular file (say, pages 3 to 7 of a 50-page report), the workflow is to extract that section first with split-pdf, then drop the smaller PDF into the merge.

If you need to rearrange individual pages after merging — interleave pages from two scans, or move a single page that ended up in the wrong spot — chain merge with organize-pdf on the result. Merge handles file-level ordering; organize handles page-level rearrangement.

What survives the merge, what changes

The visible content of every page comes through cleanly: text, images, headers, footers, layouts. Annotations like highlights, sticky notes, and link annotations are preserved. Form fields you've filled in are kept.

A few things to know:

• Bookmarks (the navigation outline on the left in PDF readers) aren't currently combined. Each input's bookmarks describe its own page numbers; merging them naively would produce broken links. The merged file comes out without an outline. If outline navigation matters for the recipient, this is a known limitation we plan to address.
• Digital signatures don't survive merging. A signature signs a specific file, and the merged document is a different file by definition. If preserving signatures is important — say, for a court filing or a notarised document — keep the signed PDFs separate and send them as multiple attachments.
• Form fields with computed defaults can lose their formula. Forms that calculate values automatically (some IRS forms, some HR templates) may copy across as flat values without the formula behind them. The visible numbers stay; the auto-recalc may not.
• Mixing PDF/A and regular PDF gives you regular PDF. If archival format compliance matters for the result, all inputs need to be PDF/A. Mixing types means the output is a normal PDF.

Practical things worth knowing

• If any of your PDFs have passwords, unlock them first. Run them through unlock-pdf before merging — encrypted files can't be read into the merge.
• Merged PDFs can grow big quickly, especially if any of the inputs are scans. If the result needs to fit an email or portal limit, run it through compress-pdf after merging.
• For very large batches (lots of files, or big files), do it on a desktop. Merging happens in your browser's memory; 50 files at 30 MB each is fine on a laptop but tight on a phone.
• If you only need parts of the merged file later, split-pdf is the inverse operation.

Where the merged packet usually goes

Most consolidated PDFs end up in one of a few places. Tax filings to the IRS, HMRC, the Australian Taxation Office (ATO), or the Canada Revenue Agency (CRA) — the main form plus supporting schedules in one upload. E-procurement portals like SAP Ariba, Coupa, the U.S. SAM.gov, the UK Crown Commercial Service, and tender systems generally — bid response in a single packet. Court e-filing — PACER and CM/ECF in U.S. federal courts, HM Courts and Tribunals Service in the UK, with strict per-document and per-filing size caps. Mortgage and credit applications at major banks, where the loan officer wants the application form, pay stubs, ID copies, and bank statements bundled. Visa and immigration packets to USCIS, UK Visas and Immigration, or IRCC in Canada — application form plus translated documents plus financial proof, all in one PDF. Most of these portals enforce a per-file size limit (5–20 MB is common); after merging, run the result through compress-pdf if it doesn't fit.

What happens to your files

Everything stays on your device. The PDFs you drop in are read into your browser's memory, the merge runs locally, and the combined PDF is offered as a download — there's no upload, no server-side processing, no copy of your file held anywhere. You can verify this by opening DevTools and watching the Network tab while you merge: there are no requests going out.