Merge PDF files

Does merging change the quality of a PDF?

No, merging here does not change quality, because every page is copied as a PDF object and nothing is converted to an image. Selectable text, embedded fonts, vector drawings and the original image resolution arrive in the merged file exactly as they were. A 300 dpi scan stays a 300 dpi scan, and a searchable contract stays searchable.

The size of the merged file is close to the sum of the source files. Fonts and images are not shared between documents that came from different files, so ten reports that each embed the same font carry ten copies of it. If the total is too large to email, run the result through Compress PDF afterwards.

How does this PDF merger work?

The merger reads each file in your browser and copies its pages, in the order shown in the list, into a brand new PDF document. The work is done by the open-source pdf-lib library inside a background Web Worker, so the page stays responsive while large files are processed. Thumbnails in the file list are drawn with Mozilla's pdf.js, also on your device.

The output is written as a standard PDF 1.7 file, the version published as ISO 32000-1, using compressed object streams to keep it compact. It opens in Adobe Acrobat, Preview, Chrome, Edge and every mobile reader. The finished file is named after the first PDF in the list with “merged” added, so it is easy to find in your downloads folder.

What is kept and what is lost when PDFs are merged?

Everything that lives on a page is kept, while document-level extras of the source files are not combined. The table below lists the common elements. If your files rely on bookmarks or fillable fields, keep the originals next to the merged copy, or flatten forms first with Flatten PDF so they look the same everywhere.

When is merging PDFs worth it?

Merging is worth it whenever several documents have to be read, printed, signed or uploaded as one unit. Typical cases are job applications with a cover letter, CV and certificates, expense claims with scanned receipts, contracts with their annexes, and course notes exported chapter by chapter. Many upload portals accept only a single attachment, which makes one combined file the only option.

One file is also easier to send and to archive. Email recipients are far less likely to miss a page when everything arrives together, and a single merged record cannot lose one of its parts in a folder. Printing becomes one job instead of five, with pages guaranteed to come out in the right order.

How do you merge PDFs on iPhone, Android, Mac and Windows?

The steps are the same on every platform: open the page in a browser, add the files, order them and press Merge. On an iPhone or iPad, tap Choose files and pick documents from the Files app or iCloud Drive; Safari saves the result to the Downloads folder in Files. On Android, the picker shows Downloads, Google Drive and any other storage app you have installed.

On a Mac or Windows PC, drag a whole selection of files from Finder or File Explorer onto the page in one go. There is no account and no upload queue, so a second batch can be merged right after the first. Older phones with little memory cope better with several small merges than with one very large one.

Tips for a clean merged file

A clean merged PDF comes from fixing order, orientation and size before or right after combining the files. These habits avoid a second round of editing and keep the combined document easy to read for the person who receives it.

• Name scans with leading numbers (01, 02, 10) and use Sort A–Z to get the right order in one click.
• Fix sideways pages before or after merging with Rotate PDF; rotation is kept when files are combined.
• If the merged file is large, run it through Compress PDF before emailing it.
• Need only part of one document? Extract those pages with Split PDF first, then merge.
• After merging, add page numbers so readers can refer to pages of the combined document, which the originals' own numbering no longer matches.

Why does a file refuse to merge?

A file usually refuses to merge because it is encrypted or damaged. Password-protected PDFs are flagged in the list and have to go through Unlock PDF first. Files that were cut off during download or saved by faulty software may not open at all; Repair PDF can often rebuild them so they merge normally.

If the browser tab reloads or stalls during a very large merge, the device has run out of memory. Each file may be up to 200 MB, but the total has to fit in the memory the browser gives the tab. Close other tabs, merge in two halves and then merge the two results, or switch to a laptop.