PDF Merge

Merging PDFs combines two or more separate PDF files into a single document, preserving all pages, layout, and most metadata. It is one of the most common PDF tasks in offices, schools, and freelance work, and yet many tools force you to upload sensitive contracts, tax forms, or medical records to a remote server. ToolHub merges PDFs entirely inside your browser using the well-known pdf-lib library, so the files never touch a server.

You can drop two PDFs or twenty, drag them into the order you want, and download the merged result with one click. Internal links, bookmarks, fonts, and images are all preserved.

1. 1

   Add your PDFs

   Drop two or more PDF files into the upload area, or click to browse. You can add files in batches if you have many.
2. 2

   Reorder the files

   Use the up and down arrows next to each file to set the merge order. Pages from each file are concatenated in the order you set, top to bottom.
3. 3

   Merge and download

   Click the merge button. The merged PDF is generated in your browser and downloads automatically as merged.pdf. Open it to verify the order before sharing.

A PDF file is structured as a tree of objects: pages, fonts, images, metadata, and a table that maps everything together. Merging is not as simple as concatenating two files end to end. The merger has to parse each source PDF, copy its pages and all the resources those pages reference (fonts, embedded images, color profiles), avoid collisions in object IDs, and rebuild the cross-reference table for the new document. The pdf-lib library handles all of this in pure JavaScript, which is why merging works entirely in your browser without needing to upload to a server.

What is preserved

• All pages in the order you specify
• Embedded fonts and images at original quality
• Internal links between pages from the same source file
• Page sizes and orientations (portrait or landscape mixed is fine)
• Most form fields if the source PDFs were created consistently

What may not be preserved

• Cross-document links (links from page in file A to page in file B will not work)
• Some advanced interactive features like JavaScript actions
• Digital signatures (these will be invalidated since the document changed)
• Some accessibility tags from older PDF versions

Is there a limit on file size or page count?

No hard limit. The merger is constrained only by your device memory. On a modern laptop, merging dozens of PDFs totaling hundreds of megabytes usually takes a few seconds. Very large jobs (several gigabytes) may slow down or fail in browsers with strict memory limits.

Will the merged file be larger than the sum of inputs?

Usually about the same. pdf-lib does not re-compress images or fonts, so the output size is roughly the sum of inputs minus duplicate embedded resources. If you need a smaller file, run the result through a PDF compression tool afterward.

Can I merge password-protected PDFs?

Not directly. You will need to remove the password from each source PDF first using your PDF reader, then merge the unlocked copies.

Does merging affect the quality of pages?

No. Pages are copied byte-for-byte where possible. Text stays selectable, images stay sharp, and any vector content remains resolution-independent.