How to Compress a PDF Without Losing Quality

A 40 MB PDF will bounce off most email attachments. Before you reach for a compressor, it helps to know why your file is big — because the right fix depends on the cause.

Why PDFs get large

• Scanned pages. A page scanned at 300 dpi as a colour image can be 2–5 MB on its own. This is the most common cause by far.
• Uncompressed images. Screenshots pasted in at full resolution, or PNGs used for photographs.
• Embedded fonts. Each embedded font adds 50–300 KB, and a document can carry dozens.
• Many revisions. PDFs can keep old versions of objects around after edits.

What compression actually does

The most effective method for scanned or image-heavy documents is re-rendering: each page is rasterised to a JPEG at a chosen quality, then the pages are assembled into a fresh PDF. Lower quality means a smaller file. Text stays perfectly readable down to roughly 60% quality; below that, small type starts to smear.

Expect roughly these outcomes:

• Quality 80–90%: 20–40% smaller, visually near-identical.
• Quality 60–70%: 50–70% smaller, good for email and web.
• Quality 40–50%: 75%+ smaller, text gets noticeably soft — use only for proofs.

Getting the balance right

Start at 70%. Compare the result against the original at 100% zoom on a real screen, not in a thumbnail. If you can read the smallest text on the busiest page without squinting, go one step lower and check again. There is no universal "best" setting — a text-only invoice can go very low, while a photo-heavy portfolio cannot.

If the file is still too big

• Scan in greyscale or black and white instead of colour — often a 10x reduction on its own.
• Scan at 200 dpi rather than 300 dpi for documents that will only be read on screen.
• Split the document and send it in parts.
• Convert to images only if the recipient just needs to look at the pages.

What not to expect

Compression cannot preserve a text layer if the method rasterises pages. Once a page becomes an image you can no longer select or search its text. If the recipient needs to copy text, compress before scanning quality is lost, or keep the original alongside the compressed copy.

Try it now: Compress PDF · PDF to JPG