pdftk (PDF Toolkit) operates at the object level. A PDF file is a collection of numbered objects — pages, fonts, images, annotations, and bookmarks — linked by a cross-reference table. When merging, pdftk reads all objects from each input PDF, renumbers them to avoid collisions, updates the cross-reference table, and writes a new combined PDF. Crucially, it does not decode or re-encode any content — images and text streams are copied verbatim, preserving exact quality.
Free PDF Merger — Online
Merge Multiple PDFs into One Combined Document
Combine two or more PDF files into a single PDF. Drag to reorder files before merging — upload order becomes the page order in the final document.
Up to 20 PDF files at once
Drag to reorder before merging
Preserves bookmarks & links
Upload order = merge order. Drag tiles to rearrange before merging.
Drop multiple files here
or browse files
Add at least 2 files • They will be combined in order
Files to combine (drag to reorder):
Add at least 2 files to enable
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Files deleted in 2h
Fast processing
No signup needed
Simple & Fast
How to Use PDF Merger
Convert your files in three simple steps — no software, no signup.
01
Upload Your PDFs
Select two or more PDF files. The upload order sets the initial merge order — you can drag to rearrange them.
02
Arrange the Order
Drag each PDF tile to the correct position. The numbered order shown is the order pages will appear in the merged PDF.
03
Download Merged PDF
Click Merge and download your combined PDF. All pages, bookmarks, and internal links are preserved.
Features
Why Use PDF Merger?
Up to 20 Files
Merge up to 20 PDF files in a single operation. Combine invoices, reports, chapters, or scanned pages with ease.
Drag-to-Reorder
Rearrange files in any order before merging. The visual order in the uploader matches the final document order.
Bookmarks Preserved
Bookmarks (outlines) from each source PDF are preserved and merged into the combined document's outline.
Internal Links Intact
Internal hyperlinks within each original PDF are offset to the correct page in the merged document.
Secure Document Handling
All uploaded PDFs are processed in an isolated session and deleted within 2 hours — never stored or shared.
Fast Merging via pdftk
Powered by pdftk-java — merges 20 PDFs in under 5 seconds without re-rendering or re-encoding any content.
Compatibility
Supported Formats
All the formats you need, all in one place.
| Format | Description | Extension | Best Used For |
|---|---|---|---|
| PDF INPUT | Standard PDF files as merge source | .pdf |
Any PDF file (scanned, digital, forms) |
| PDF/A INPUT | Archival PDF/A files as merge source | .pdf |
Legal and government archival documents |
| PDF OUTPUT | Single merged PDF document | .pdf |
Combined reports, proposal packets |
| PAGE RANGE | Optional: include only specified pages | — |
Selective merge from multi-page PDFs |
| REVERSE ORDER | Optional: merge files in reverse order | — |
Reverse scan order correction |
FAQ
Frequently Asked Questions
Free users can merge up to 20 PDFs per operation, each up to 100 MB. The total combined size must be under 500 MB.
Yes. Pages within each PDF are always kept in order. You control the order of entire files relative to each other by dragging tiles in the uploader.
Enter the password for each protected file in the corresponding field. PDFs with edit or print restrictions can typically be merged without a password.
Yes. Form fields and digital signatures are carried through the merge without modification. Note that interactive form fields across merged PDFs may have duplicate field names.
Usually the merged file is approximately the sum of inputs. pdftk does not re-encode content, so there is no quality loss and minimal overhead beyond a shared cross-reference table.
Yes. Specify a page range for each uploaded file (e.g., pages 1–5 from File 1, pages 3–7 from File 2). Leave the range empty to include all pages.
Real-World Uses
Who Uses PDF Merger?
From everyday users to professionals — see how people rely on this tool every day.
Legal Professional
Assemble Contract Packets
Merge a main contract PDF with exhibits, addenda, and signature pages into a single numbered document for filing.
Accountant
Combine Invoice Scans
Merge monthly invoice scans into a single PDF for expense reports, accounting records, or tax submissions.
Publisher
Compile Multi-Chapter Documents
Merge separately authored chapter PDFs into a single publication-ready document with unified numbering.
Project Manager
Bundle Project Deliverables
Combine specification, design, and test report PDFs into one deliverable package for client review.
Student
Merge Assignment Attachments
Combine your essay, bibliography, and appendix as separate PDFs into one submission file.
Admin Staff
Consolidate Scanned Pages
When a scanner outputs one PDF per page, merge them all into a single multi-page document in seconds.
Why TransmuteBox?
TransmuteBox vs. Alternatives
See how we compare to desktop software and other online converters.
| Feature |
Our Tool TransmuteBox |
Adobe Acrobat | Other Online |
|---|---|---|---|
| Merge up to 20 PDFs at once | Often limited | ||
| Drag-to-reorder before merging | |||
| Bookmarks preserved in output | |||
| Internal links preserved | |||
| Page range selection per file | |||
| No quality loss (no re-encoding) | |||
| No watermark on output | |||
| Free to use |
Under the Hood
Technical Specifications
Built on industry-standard open-source tools for maximum quality and reliability.
Limits & Restrictions
- Max 20 PDFs per merge operation
- Max 100 MB per individual file
- Max 500 MB total combined input size
pdftk
PDF
Merge
Combine
Document Assembly
Conversion Engine
pdftk-java — byte-level PDF concatenation without re-rendering
Output Quality
Zero quality loss — pages are copied byte-for-byte from originals
Average Speed
Typical: under 5 s for 20 files; speed depends on total combined file size
Data Security
HTTPS transfer · isolated temp dir · auto-purged in 2 h
Max files
Up to 20 PDFs per operation
File size
100 MB per file · 500 MB total
Processing
No re-encoding — pure byte-level merge
Complete Guide
How PDF Merging Works: pdftk, Page Structure, and Preserving Bookmarks Across Documents
Merging PDFs sounds trivial — it's just concatenating pages — but the internal PDF cross-reference structure, bookmarks, and link annotations all require careful handling to produce a correct combined document.
How pdftk Merges PDFs
Bookmarks (Outlines) Across Merged Documents
PDF bookmarks (called "outlines" in the specification) are stored as a tree of destination objects that point to specific pages. After merging, page numbers shift — what was page 1 of the second document may now be page 15 of the merged document. pdftk offsets all bookmark destinations by the correct page count, so bookmarks from each source PDF continue to point to the right pages in the merged output.
Internal Links and Cross-References
Hyperlinks within a PDF (like a table of contents linking to chapters) are stored as annotation objects with page-number destinations. The same page-offset correction applied to bookmarks is applied to all internal link annotations, ensuring that "click to go to Chapter 3" still works after merging. External URLs in PDFs are unaffected as they are absolute references.
File Order and the Drag-to-Reorder Interface
The order of pages in the merged PDF is determined entirely by the order in which you provide the input files. TransmuteBox's uploader renders each file as a draggable tile showing the file name and page count. The numbered order displayed exactly matches the output — file 1 starts at page 1, file 2 follows immediately after file 1's last page, and so on. Reordering before merging takes a fraction of a second and costs nothing.
Merging Password-Protected PDFs
PDFs can have two kinds of passwords: a user (open) password that must be entered to view the file, and an owner password that restricts printing, copying, or editing. pdftk can merge PDFs that have owner restrictions without a password in most cases. User-password-protected PDFs require the password to be entered for each file individually. The merged output is created without any password — apply a new password separately using the PDF Converter options if needed.