PDF Merger

Merge multiple PDF files into one online for free. No sign-up, no watermark.

✓ Free✓ No sign-up✓ Works in browser

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Add multiple PDFs — they will be merged in order

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How to Use This Tool

Upload PDFs

Upload 2 or more PDF files using the upload button or drag and drop. There is no limit on the number of files.

Reorder as Needed

Drag and drop the files into the order you want them to appear in the merged document. Thumbnail previews show the first page of each file.

Merge and Download

Click Merge PDF. Download your combined PDF file instantly — no email required.

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Frequently Asked Questions

How many PDFs can I merge at once?

There is no hard limit. You can merge as many PDFs as you need. For very large batches (50+ files), processing may take a minute.

Can I merge password-protected PDFs?

No. Password-protected PDFs cannot be merged. Remove the password protection first using our PDF Password Remover tool.

Will the merged PDF preserve bookmarks and links?

Yes, bookmarks and internal links from the original PDFs are preserved in the merged output.

Can I select specific pages to merge?

For page-level selection, use our PDF Splitter first to extract the pages you want, then merge those extracted files.

About PDF Merger

Your accountant sent the signed engagement letter, the W-9, and two bank statements as four separate PDFs, and the client portal only accepts a single upload per document slot. Or you are assembling a grant application where the RFP explicitly requires exhibits A through F combined into one file under 10MB because the agency's intake MTA rejects anything larger. This merger uses pdf-lib.js running entirely in your browser — the PDFs are read into an ArrayBuffer via FileReader, stitched page by page into a new PDDocument, and written out as a single downloadable Blob. You can drag to reorder, preview thumbnails before committing, and it preserves outline bookmarks and most interactive form fields (AcroForm, not XFA). Merge order matters because the table of contents and any cross-document internal links are rewritten against the new page numbers. Files never leave the tab, which matters when the documents are under NDA or contain financial data you cannot hand to a random SaaS uploader.

When to use this tool

Assembling a signed contract package

A freelancer collects a 4-page MSA, a 2-page SOW, a 1-page W-9, and a 1-page certificate of insurance from four different DocuSign envelopes. Merge in legal-review order so the client's procurement team sees the master agreement first, saves as one 420KB PDF ready for upload to their AP portal.

Combining scanned receipts for an expense report

A consultant has 18 hotel and taxi receipts scanned as individual PDFs from a Fujitsu ScanSnap. Merge them into a single file sorted by date, attach to the expense report in Concur, which rejects more than three attachments per line item.

Building a board meeting binder

A corporate secretary receives the agenda, CEO update, financials, and four committee reports as separate PDFs the night before a board meeting. Merge into a single 80-page binder with bookmarks preserved so directors can jump to each section from the outline pane in Adobe Reader.

Submitting a grant application under attachment limits

A nonprofit's federal grant portal requires exhibits A through F as a single PDF under 10MB. Merge six exhibit documents (total 6.2MB raw), then run the combined output through the pdf-compressor if it crosses the threshold after merge.

Creating a case file for a paralegal handoff

A litigator compiles 12 exhibits, two deposition transcripts, and a complaint into one chronological PDF before forwarding to opposing counsel. Reordering during merge preserves the exhibit lettering that the trial exhibit list references.

How it works

1
Each PDF is parsed into a pdf-lib PDDocument
FileReader reads every selected file as an ArrayBuffer, then pdf-lib's PDFDocument.load parses the cross-reference table, object streams, and catalog. We intentionally skip updateMetadata so any existing /Info dictionary entries (Author, CreationDate) from the first document carry through to the output instead of being overwritten with generic defaults.
2
Pages are copied, not re-rendered
For each source document we call copyPages(src, indices) which deep-copies the page tree including content streams, resource dictionaries, and embedded fonts. Because there is no rasterization step, text remains selectable, vector logos stay crisp, and file sizes stay close to the sum of inputs rather than ballooning like a print-to-PDF would.
3
Bookmarks and link annotations are remapped
After copying, we walk the outline tree (the /Outlines dictionary) and rewrite each destination reference against the new page objects. Internal GoTo link annotations are updated the same way. External hyperlinks (URI actions) require no change. XFA-based dynamic forms are the one thing we cannot remap cleanly and will fall back to flattened static pages.

Honest limitations

· AcroForm fields from non-first input documents are dropped to avoid field-name collisions; flatten forms before merging if you need to preserve entered values.
· XFA-based dynamic forms (older IRS forms, some government applications) cannot be merged cleanly because XFA is an XML layer pdf-lib does not process — the form surface flattens to static pages.
· Very large inputs (single files over 200MB or combined over 500MB) may exhaust browser memory on low-RAM devices because the entire document graph has to sit in the JavaScript heap simultaneously.

Pro tips

Put the document with form fields first

If one of your inputs contains AcroForm fields (a fillable W-9, a government application), place it first in the merge order. pdf-lib keeps the form dictionary from the initial document and silently drops later ones, because two forms with overlapping field names would corrupt in Adobe Reader. If you need fields from multiple sources, flatten each one individually first (print to PDF inside the source application) so the fields become static text and no dictionary conflict occurs.

Re-optimize after merge if the result is over 10MB

Merging does not dedupe fonts or images shared across inputs — if five documents each embed a 600KB version of Calibri, the merged file carries all five copies. For email attachment caps (Gmail 25MB, Outlook 20MB, many corporate MTAs 10MB) the quick fix is to run the merged output through the pdf-compressor which will subset and deduplicate fonts during re-save, often cutting size by 30 to 60 percent with no visible quality change.

Preserve original page size per document

If you merge a US Letter contract with an A4 exhibit, the output keeps each page at its original size — the merger does not force a uniform paper size. For court filings where the clerk rejects mixed page sizes, print each source to a uniform size first via your OS print dialog (set paper size to US Letter with 'fit to page') and then merge the normalized outputs. Confirm in Acrobat by opening the Document Properties dialog — the Advanced tab lists every distinct page size in the file.

Frequently asked questions

Will bookmarks and the table of contents survive the merge?

Yes for standard PDF outlines (the /Outlines dictionary). Each source document's bookmarks are copied into the output and the page destinations are remapped to the new page numbers after merging. Nested bookmark hierarchies are preserved down to any depth. The one caveat is table-of-contents pages that are themselves rendered as visible pages with internal GoTo links — those also get their link annotations remapped, but if the source TOC references a page range that no longer exists (because you skipped pages during selection) the link will become a dead reference.

Can I merge password-protected PDFs?

Only if you unlock them first. Encrypted PDFs come in two flavors: user-password-protected (needed to open) and owner-password-protected (needed to modify or print). pdf-lib refuses to load user-password files without the password, and will throw an error even on owner-password files that block modification. Unlock each input first using the pdf-password-remover tool (which requires you to know the password and have authority to remove it), then merge the unlocked copies. Never try to circumvent protection on PDFs you do not own.

Does merging affect file size beyond the sum of inputs?

The merged output is typically 2 to 8 percent smaller than the raw sum because pdf-lib rewrites the cross-reference table as a single compressed xref stream and removes orphaned objects from each input. However, duplicated resources (the same font embedded in multiple sources, the same company logo in every document's header) are not deduplicated, so a merger of ten branded documents can still be close to ten times the size of one. Run the output through the pdf-compressor when that matters for email attachment limits.

Is the merge truly local or are files uploaded?

Truly local. Every step runs in your browser tab via pdf-lib.js compiled to WebAssembly helpers for the performance-critical parsing steps. Files are loaded with FileReader into an ArrayBuffer that lives in JavaScript heap memory, processed, and the output is offered as a download via URL.createObjectURL on a Blob. There is no fetch, no websocket, no service worker upload. Close the tab and the in-memory copy is garbage collected. This matters when the PDFs contain client financials, medical records, or anything under NDA where a server-side tool would create a compliance problem.

Why did my merged PDF lose the signed signature appearance?

Digital signatures (the cryptographic kind with a /Sig dictionary, not a scanned image of a handwritten signature) invalidate the instant a document is modified, including merging. The signature's byte-range hash covers the exact file contents at signing time, and merging necessarily rewrites the cross-reference table. The visual signature stamp may still appear but Adobe Reader will show 'signature is invalid' with a yellow warning. If preserving signatures is required, send the signed file separately as its own attachment rather than merging it with others.

Merging is the first step in most multi-document workflows. Once combined, if the result exceeds email caps the pdf-compressor re-encodes images and subsets fonts to shrink the file. If you merged in the wrong order or need to extract a subset later, the pdf-splitter slices the combined file back into ranges. For scanned inputs that came in as image files before merging, the images-to-pdf tool converts JPG or PNG stacks into a PDF first so they can join the merge queue. And when the final package needs to be sent to a client, the protect-pdf tool adds the user password that procurement portals often require.