Compress PDF

1. Choose your PDF, or drop it onto the box. It is opened in your browser, so the file never leaves your device.
2. Pick a level. Recommended suits most files; see the table below.
3. Click Compress PDF and download. The tool shows the size before and after, for example 18 MB → 3.1 MB.

You get a new copy named yourfile-compressed.pdf; the original is untouched. Typed text, lines and fonts stay exactly as they were at every level; only pictures, including scanned pages, are made smaller. If a level can't make the file any smaller, the tool tells you instead of giving you the same file back.

dpi (dots per inch) is how many picture pixels cover each inch of the page. 150 dpi looks sharp on any screen and prints well enough for everyday use. 100 dpi is fine on screen, but small print inside a scanned picture can start to look fuzzy. Try Recommended first and only move to Strong if the file is still too big.

Nearly always it's the pictures. A page of typed text takes a few kilobytes, but a scanned page or a phone photo is millions of pixels. The usual causes:

• Scans saved at high resolution. Scanners and copiers often default to 300 or 600 dpi in colour, even for a plain letter.
• Photos from a phone camera pasted into a document at full size, 12 megapixels or more each.
• “Print quality” or “high quality” export settings that keep every image at full resolution.
• Embedded fonts add a little to every file, but rarely more than a megabyte or two.

Halving the resolution leaves a quarter of the pixels, which is why going from a 300 dpi scan to 150 dpi makes such a difference. A PDF that is only text and drawings is already small; Light can tidy it up, but don't expect a big drop.

The limit is for everything attached to one email, and the receiving server has its own limit too, so a 24 MB file that leaves Gmail can still bounce. To be safe, keep email attachments under 10 MB. For an upload form, check the limit printed next to the upload button and compress until the result is below it.

• Try Strong on the original file. Compressing an already compressed copy again gains little and costs quality.
• Remove pages you don't need, such as blank backs of scanned sheets, with Delete PDF pages, or keep only the pages the recipient asked for with Extract PDF pages.
• Send it in parts: extract the first and second half into separate files and send two emails.
• Share a link from Google Drive, OneDrive, iCloud or Dropbox instead of attaching the file.
• Scan again at a lower setting. For a typed letter, 150 dpi in greyscale is plenty and makes a far smaller file from the start.