RunToolRunHow to Merge PDF Files
Select your PDFs
Click the upload area or drop two or more PDF files. The order you select them is the order they are merged.
Merging runs in your browser
All pages are copied into a single new document on your device — contracts and reports never touch a server.
Download the merged PDF
Save one combined file containing every page of every input document.
Merging is a structural operation, not a re-render
A PDF is an object graph: pages reference fonts, images, colour profiles and content streams stored elsewhere in the file. Merging done properly copies those page objects and every resource they depend on into a new document and rebuilds the cross-reference table that tells a reader where each object lives.
That distinction matters because it means nothing is re-encoded. Text stays as text, vector diagrams stay as vectors, and image quality is untouched — the bytes describing page three of your second file are the same bytes in the merged output. A merged PDF is therefore lossless, and its size is roughly the sum of the inputs minus whatever resources the files had in common.
Why the merged file is sometimes larger than expected
If two source documents each embed the same 3 MB font subset or the same letterhead image, a naive merge stores both copies. Deduplication of identical resources is possible but not guaranteed, so a merge of five reports from the same template can land noticeably above the sum you predicted.
The reverse also happens. PDFs often carry incremental-update history: every save appends a new revision while leaving the old one in the file. Rebuilding the document during a merge writes a single clean revision and discards that history, which can make the output smaller than the inputs combined — and quietly removes earlier versions of edited content, which is usually what you want.
Order, rotation and page size
Pages are appended in the order the files are listed, so the arrangement you set before merging is exactly what you get. Mixed page sizes are preserved rather than normalised — an A4 report followed by a US Letter appendix stays that way, and each page keeps its own dimensions. Readers handle this fine; some printers do not, so check the print preview if the merged file is destined for paper.
Rotation is stored as a page attribute rather than baked into the content. A page that was scanned sideways and rotated in a viewer carries that rotation with it into the merge, which is why a page can look correct in one reader and sideways in another if the original rotation flag was inconsistent.
What does not survive a merge
Interactive features are the casualty. Form fields from different documents can collide when two files use the same field names, and the merged result may show linked fields that update together or fields that lose their values entirely. Digital signatures always break: a signature certifies a specific byte sequence, and merging necessarily changes it.
Bookmarks, internal links and attachments may or may not be carried across depending on how the merge is performed. If a document's internal navigation matters, check it in the output rather than assuming — and if the file is signed, merge before signing rather than after.
Encrypted files and where the work happens
A password-protected PDF cannot be merged without being decrypted first. Owner passwords that only restrict printing or copying are a different matter from user passwords that encrypt the content: the second kind must be removed before the pages can be read at all.
The merge runs entirely in your browser, so contracts, medical records and financial statements are never uploaded. The practical limit is your device's memory rather than a server quota — a few hundred pages is comfortable, while merging several very large scanned documents at once is where a laptop starts to struggle.