PDF Merge
Combine multiple PDF files into a single document. Drag to reorder pages before merging.
Combine multiple PDF documents into a single unified file. Reorder pages in the queue and merge locally inside your browser.
Drop PDF files here to merge
or click to select 2 or more PDF files
Document Merge Queue (0 files)
How do I use PDF Merge?
Drop two or more PDF files into the upload zone, or click "Load Sample Data" to generate sample PDFs.
Drag and drop the document cards to reorder pages or remove unwanted files.
Click "Merge PDF" to combine all documents client-side and download the unified PDF.
What features does PDF Merge offer?
Merge multiple PDF documents into a single file with 100% vector stream retention
Interactive queue reordering with intuitive up and down document sequence controls
Dual-engine architecture: In-browser pdf-lib client engine or 500MB high-throughput Cloud Engine
Full preservation of embedded TrueType/OpenType font subsets, bookmarks, and internal links
One-click sample PDF generator to test document combining without uploading local files
Seamless support for mixed page dimensions, including US Letter, A4, and Legal orientations
ISO 32000-1 (PDF 1.7) Cross-Reference (`xref`) & Object Tree Merging
Merging PDFs combines independent `/Catalog` page trees and re-indexes indirect object numbers (`N 0 obj`) into a single unified cross-reference table.
| PDF Structure Object | ISO 32000-1 Dictionary Key | Merge Engine Behavior | Edge Case / Constraint |
|---|---|---|---|
| Page Tree Nodes | /Type /Pages & /Kids [...] | Clones page references in user-defined order | Preserves mixed portrait/landscape MediaBox |
| Embedded Fonts | /FontDescriptor & /BaseFont | Retains subsetted font streams per source | Duplicate font subsets increase size slightly |
| AcroForm Interactive Fields | /AcroForm /Fields [...] | Copies widget annotations; flattens collisions | XFA dynamic XML forms require flattening |
| Encryption Dictionary | /Encrypt (RC4 / AES-128 / AES-256) | Rejects owner/user password-locked streams | Unlock encrypted PDFs prior to merging |
Frequently Asked Questions about PDF Merge
Why does merging two PDFs with different page sizes (A4 and US Letter) preserve both sizes?
Each `/Page` dictionary in a PDF defines its own independent `/MediaBox` and `/CropBox` in PostScript points (`1 pt = 1/72 inch`). Merging preserves every page's exact native dimensions and orientation without scaling or cropping.
Can password-protected or AES-encrypted PDF files be merged in the browser?
Files with an open User Password cannot be parsed without decryption. Documents with only an Owner (permissions) password or unencrypted streams merge seamlessly inside browser memory.
What is the maximum file size and page count supported for client-side PDF merging?
Because processing happens inside an isolated WebAssembly/JavaScript ArrayBuffer without server uploads, you can merge up to 50 PDF files or 150 MB total payload depending on available device RAM.
Are interactive hyperlinks and internal bookmarks preserved when merging PDFs?
External URI `/Action` links (`/S /URI`) on individual pages are preserved intact, while document-level `/Outlines` are rebuilt around the merged page index sequence.
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