Fusionneur PDF

When you merge PDF files, the merger takes each source document and copies its pages — along with all embedded fonts, images, vector graphics, and content streams — into a single new PDF file. The pdf-lib library performs this at the page level, meaning each page from each source file is appended to the output in the order you specify. The result is a single, contiguous PDF document that preserves every visual element from the original files.

Importantly, this process is lossless. Unlike re-saving a JPEG or re-encoding a video, merging PDFs does not re-compress or re-encode any content. The fonts, images, and vectors in the merged output are byte-for-byte identical to those in the source files. This is why the merged file size is approximately the sum of the input file sizes — no data is added or removed, only reorganized into a single container.

Merging is the right choice when you have multiple PDF files that you want to combine into a single document for sending, archiving, or sharing. Common scenarios include combining signed contract pages, assembling invoice bundles for accounting, or creating a complete HR onboarding packet from individual forms.

If you need to combine images (JPG, PNG) into a PDF, use our Image to PDF tool instead — it handles image-to-page conversion with options for page size, orientation, and margins. If you need to extract specific pages from a large PDF, use our Split PDF tool. And if your merged PDF is too large to email, run it through our PDF Compressor to strip redundant metadata and optimize the structure.