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Merge PDF
Merge PDF combines two or more PDF files into a single document using the pdf-lib engine running in your browser. Pages are copied in the exact order you arrange them, and every source file keeps its original page size, embedded fonts and vector artwork. Nothing is rasterised, so the merged file stays as sharp as the originals.
How to use Merge PDF
- Drag several PDF files onto the drop zone, or use the file picker to select them.
- Reorder the queue with the up/down controls until the sequence matches the document you want to produce.
- Press Process to concatenate the documents, then download the combined PDF.
Where Merge PDF is useful
- Assembling one submission pack from a cover letter, CV and scanned certificates.
- Appending monthly invoices or bank statements into a single archive file.
- Combining chapters that were exported separately from a word processor.
Formats, algorithms and limits
Merging is a page-tree operation: pdf-lib copies the page objects and their resources into a new document, which preserves text selectability, form fields in most cases, bookmarks that live inside each file and vector graphics. Because nothing is re-compressed, the merged file is usually close to the sum of the inputs.
Troubleshooting and honest limits
- Password-protected files must be unlocked first — encrypted PDFs cannot be parsed by the merge engine.
- Very large merges (hundreds of MB) depend on available browser memory; close other tabs if the tab slows down.
- Internal links and bookmarks are preserved per document but are not re-mapped into one continuous outline.
Frequently asked questions
In what order does the merge place my files?
Exactly the order shown in the upload queue, top to bottom. Use the move controls to rearrange files before running the merge; the queue order is the page order of the output.
Will merging reduce the visual quality of my PDFs?
No. Pages are copied as vector objects rather than re-rendered, so text, line art and fonts are byte-identical to the source files and file size is roughly the sum of the inputs.
Can I merge PDFs that have different page sizes?
Yes. Mixed A4, Letter or custom sizes are kept as-is; each page retains its own dimensions instead of being scaled onto a single sheet.
Why did my merge fail with a protected file?
Encrypted PDFs block the parser. Run the file through the Unlock PDF tool first (only for documents you own or are permitted to modify), then merge the decrypted copy.
Related tools
Page written and reviewed by the FreeConvertio engineering team on 2026-10-14. Merge PDF runs entirely in your browser — no uploads, no account and no daily limits.