Merging PDFs combines multiple separate PDF files into a single document. This is useful for assembling reports, combining invoices, packaging contracts with attachments, or consolidating research materials.
Why merge PDFs?
Common use cases:
- Combine a cover letter and resume into one file for job applications
- Merge monthly reports into a single annual document
- Package a contract with its exhibits and addenda
- Combine scanned pages into one multi-page document
- Assemble a presentation with supporting appendices
How PDF merging works
A PDF file is a structured document containing pages, fonts, images, and other resources. When you merge PDFs, the process:
- Reads each source PDF's page objects
- Renumbers pages sequentially
- Merges embedded fonts and resources into the output document
- Writes all pages into a single new PDF file
The resulting file contains all pages from all source files, in the order you specify.
Page size consistency
PDF pages can have different sizes — A4, Letter, Legal, or custom dimensions. When merging PDFs with mixed page sizes, the output preserves each page's original dimensions. This means:
- An A4 page remains A4 in the merged file
- A Letter-size page remains Letter-size
- Viewers display each page at its native size
If you need all pages at the same size (for printing or professional presentation), you'll need to resize pages before or after merging using a PDF editor.
Standard page sizes
| Size | Width × Height | Common use |
|---|---|---|
| A4 | 210 × 297 mm | International standard |
| Letter | 216 × 279 mm | US standard |
| Legal | 216 × 356 mm | US legal documents |
| A3 | 297 × 420 mm | Large format |
Fonts and embedded content
PDFs can either embed fonts (include the complete font data in the file) or reference system fonts (assume the reader has them installed). When merging:
- Embedded fonts are preserved in the merged document
- Referenced fonts may not display correctly if the viewer doesn't have them
- Images, vector graphics, and form fields are preserved
For maximum compatibility, use PDFs with embedded fonts as source files.
File size after merging
The merged PDF's size is roughly the sum of the source files, minus any duplicate embedded resources that can be deduplicated. In practice:
- Two 1 MB PDFs → approximately 2 MB merged
- PDFs sharing the same embedded fonts may be slightly smaller than the sum
- Image-heavy PDFs contribute most to file size
If file size is a concern, compress the merged PDF afterward.
Privacy when merging PDFs
Many online PDF tools upload your files to remote servers for processing. This is a significant privacy risk for:
- Legal documents with sensitive clauses
- Financial statements
- Medical records
- HR documents and contracts
- Any document marked confidential
Browser-based PDF merging processes files entirely in your browser using JavaScript — your documents never leave your device.
How to merge PDFs free
- Go to PDF Merger
- Click Add Files or drag and drop your PDF files
- Drag to reorder the files if needed
- Click Merge PDFs
- Download the combined PDF
All processing happens in your browser — your PDFs are never uploaded to any server.