Combine multiple PDF files into one document
A PDF is not a single continuous stream and it is a collection of numbered page objects plus metadata (bookmarks, form fields, embedded fonts, images) tied together by a cross-reference table. Merging PDFs is therefore not string concatenation; it is building a new PDF whose page tree references the right subset of objects from each source file, with the cross-reference table rewritten so page numbering, internal links, and bookmarks stay consistent. A naive concatenation of two PDFs produces a file that either will not open or shows only the first source's pages. This merger handles the object rewriting correctly. Upload any number of source files (tested up to roughly 500 MB of combined input in typical browser memory), reorder them by dragging, and export a single output with sequential page numbers. Embedded fonts are deduplicated so a report combining ten documents that all use Helvetica does not store ten copies of the font. Bookmarks from each source are preserved and grouped under a per-file heading in the output table of contents. Form field names are namespaced to avoid collisions when two source files both have a field called "signature".
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Combine multiple audio files into one track. Drag and drop to reorder, merge MP3s, WAVs, and other formats. Create seamless audio compilations online.
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Convert multiple images into a single PDF document. Drag and drop to reorder pages, customize page size, orientation, and margins.
A signed contract, an appendix, and a cover letter are three PDFs that must go to the client as one document.
Input
cover.pdf + contract.pdf + appendix.pdf (drag to order)
Output
bundle.pdf, pages in the set order, bookmarks preserved
Pages are concatenated in the order you arrange them while keeping each source’s page size and internal links intact. It runs in the browser, so a confidential contract is never uploaded.
A PDF is not a single continuous stream and it is a collection of numbered page objects plus metadata (bookmarks, form fields, embedded fonts, images) tied together by a cross-reference table. Merging PDFs is therefore not string concatenation; it is building a new PDF whose page tree references the right subset of objects from each source file, with the cross-reference table rewritten so page numbering, internal links, and bookmarks stay consistent. A naive concatenation of two PDFs produces a file that either will not open or shows only the first source's pages. This merger handles the object rewriting correctly. Upload any number of source files (tested up to roughly 500 MB of combined input in typical browser memory), reorder them by dragging, and export a single output with sequential page numbers. Embedded fonts are deduplicated so a report combining ten documents that all use Helvetica does not store ten copies of the font. Bookmarks from each source are preserved and grouped under a per-file heading in the output table of contents. Form field names are namespaced to avoid collisions when two source files both have a field called "signature".
Combine cover page, table of contents, chapters, and appendices from separate files into one polished report.
Merge monthly invoices into a single document for accounting or client records.
Join a resume, cover letter, and reference letters into one PDF for job or grant applications.
Combine exhibits, declarations, and forms into the required filing order.
The merger works on the PDF object model directly using pdf-lib, parsing each source's cross-reference table and page tree, then constructing a new document whose /Pages root references the selected pages from each input. Because the page content streams (the actual drawn marks) are copied by reference rather than re-rendered, output pages are pixel-identical to source pages, no quality loss, no re-encoding of embedded images. A 10 MB document merged from a 4 MB and 6 MB source typically ends up within a few kilobytes of the sum, with the small difference coming from deduplication of shared resources like fonts and color profiles.
Page sizes are preserved per page, not normalized. A document merging A4 and US Letter sources will have mixed page sizes in the output, matching each source's original dimensions. This is usually what you want for reports combining documents from different regions. If you need uniform page size, process the non-matching files through a PDF resizer first or use a print-to-PDF step to rasterize to a single size (at the cost of quality on vector content).
One gotcha with encrypted PDFs: the merger cannot copy pages from a document you do not have the decryption key for. Password-protected PDFs must be unlocked first using the PDF Password Protector tool before they can be merged. Digital signatures are a related issue, a signed PDF, by design, has a signature that covers the entire document hash, so merging a signed PDF into a new document invalidates that signature. The merger preserves the visual signature (the drawn signature box stays on the page) but the cryptographic validity is lost. This is a limitation of the PDF signing standard, not the merger.
There is no hard limit. Performance depends on your browser and the total file size, but merging dozens of typical documents works smoothly.
Yes. Bookmarks from each source file are preserved in the final document.
You will need to remove the password first. Use the PDF Password Protector tool to unlock files before merging.
PDF parsing and editing happen in your browser. Documents, and everything inside them, are never uploaded or stored remotely.