Merge PDF

Merging combines several PDF files into one document by copying every page from each source into a single new file. The tool reads each input, walks its page tree (the structure defined in the PDF 1.7 specification, ISO 32000-1), and appends the pages to a fresh document in whatever order you arranged them. Fonts, embedded images, and bookmarks come along; cross-document hyperlinks usually do not, because they were anchored to filenames that no longer exist.

Drag the files into the upload zone, reorder them by dragging the thumbnails, and press merge. A common workflow is assembling a coursework portfolio at 11pm: cover sheet PDF, three essays exported from Word, a scanned signed declaration, and a bibliography. Five files in, one file out, ready for the upload deadline.

Some PDFs cannot be merged. Files protected with a user-password (the one a viewer prompts for on open) cannot be read at all without that password. Files with owner-password restrictions can sometimes be processed, depending on what permissions the owner set. Encrypted PDFs from corporate document management systems often refuse to merge until the encryption is removed.

Form fields are another snag. If two PDFs both contain a field called 'Name', the merged file will have two fields with the same name, and most viewers will mirror typing in one to the other. To avoid this, [Flatten PDF](/flatten-pdf) each source before merging so the fields become static content.

All merging runs in your browser using pdf-lib. The documents never reach a server, which is the right setting for confidential bundles: payslips, tenancy agreements, divorce paperwork, anything you would not want sitting in a third-party log. The trade-off is browser memory; merging twenty large scanned PDFs at once on a phone can hit limits. On a laptop, files totalling a few hundred MB usually merge in seconds.