How to merge PDF files
- Drop two or more PDFs into the box above, or choose them from a folder.
- Put them in order: drag a file up or down, or use its arrow buttons. Add more files at any time.
- Select Merge, then download the combined PDF.
How it works
Merging uses pdf-lib, an open-source PDF library, in a background thread so the page stays responsive with large files. It creates a new, empty PDF, then opens your files one by one in the order you set and copies every page across.
A PDF page is a set of objects: drawing instructions, fonts and images. Copying moves those objects as they are, with nothing rendered or re-compressed. That's why text stays selectable, scanned pages keep their exact image quality, and each page keeps its own size and rotation. It also means the merged file is roughly as big as the files added together; if it's too big to send, compress it afterwards.
Only pages are copied, so a few things that belong to a whole document don't come along:
- Bookmarks (the outline in a viewer's sidebar) aren't carried over.
- Fillable form fields keep how they look but can stop working as fields, because the form's list of fields isn't merged. Fill and save forms before merging.
- Document properties such as title and author start fresh, and files attached inside a PDF are left out.
Password-protected PDFs can't be read without the password, so they're stopped with a message;unlock them first. Each file can be up to 200 MB.
Good to know
- The merged file keeps every page exactly as it was: text stays selectable and images keep their quality.
- Page sizes can differ. A letter-size invoice and an A4 contract can sit in the same PDF, each at its own size.
- Want only some pages from a file? Split it or delete pages first, then merge.
- Merging photos rather than PDFs? Use JPG to PDF.
Common uses
- Application documents in one file. A job or visa application asks for a single PDF, but your CV, cover letter and certificates are separate files. Merge them in the order the form asks for.
- Invoices for your accountant. Merge a month's invoices or statements into one file, so your accountant or finance team gets everything in a single attachment.
- Adding a cover page. Put a cover sheet or title page in front of a report by merging the two files with the cover at the top of the list.
- Chapters into one document. Chapters or sections exported as separate PDFs can be joined into one document to read, share or print in one go.
From the blog
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