Compress PDF

How this compressor works, and what it costs you

Be clear about the trade before you use it. This tool renders each page to an image at a reduced resolution, compresses that image as JPEG, and rebuilds the document from those images at the original page dimensions. It is the same technique as printing to PDF at a lower quality.

The consequence is that text stops being text. In the compressed file you cannot select, copy or search the words, and a screen reader cannot read them. Vector graphics are flattened, so zooming in shows pixels where the original stayed crisp.

For a scanned document this costs you nothing, because the pages were already images — you are simply storing them more efficiently. For a text document generated by Word or LaTeX, it costs you a great deal, and the size reduction is often disappointing because text compresses badly as an image.

When compressing is the right move

Scanned paperwork is the clearest case. Scanners default to 300 or 600 DPI in full colour, which produces enormous files for what is usually black text on white paper. Dropping to 120 DPI at quality 72 routinely cuts such a file by 80–95% while leaving it perfectly legible.

Photo-heavy documents — portfolios, property brochures, reports full of screenshots — also compress well, because the content is photographic to begin with and JPEG is designed for exactly that.

Presentation exports sit in between. Slides are usually a mixture of large background images and a little text, so they shrink substantially but the text softens. Preview the result before sending it.

Text-only documents are where you should stop and reconsider. A 200-page text PDF is usually only a few megabytes already, and rasterising it may make it larger while destroying searchability.

Choosing a level

Light (150 DPI, quality 85) keeps scanned text sharp enough to read comfortably on screen and to print acceptably. Use it when the document still has to look professional.

Balanced (120 DPI, quality 72) is the setting that solves most email-attachment problems. Text remains clearly legible; fine detail in photographs softens a little.

Strong (96 DPI, quality 60) is for when a hard limit must be met. Text is still readable but visibly degraded, and photographs show obvious JPEG artefacts. Check the output before sending it to anyone important.

Custom lets you tune both independently. Resolution controls how much detail survives; quality controls how much compression noise is added. For text-heavy scans, keeping DPI up and quality down usually looks better than the reverse.

If this is not enough

Compression works page by page, so removing pages you do not need is often the bigger win — a 60-page report where you only need 4 pages should be split rather than compressed.

Colour matters too. A colour scan of a black-and-white document carries three channels of information for content that needs one. Rescanning in greyscale, where that is an option, typically beats any amount of after-the-fact compression.

And if the file must stay searchable, do not use this tool at all. Split out the pages you need, or ask whoever sent it for a smaller original.