How to Reduce PDF File Size
Almost all PDF bloat comes from one place, and once you know which, choosing a compression setting stops being guesswork.
Published 2026-07-22 · Trump PDF
Why your PDF is so large
Text is tiny. A page of pure text is often a few kilobytes because it stores characters and font references, not pictures. Images are what make files heavy, and scans are nothing but images — a scanner producing a full-colour 300 dpi page can generate several megabytes per sheet. If your document came from a scanner or a phone camera, effectively 100% of its size is image data. Embedded fonts, thumbnails and revision history add a little more.
What compression actually changes
For image-based PDFs, two levers do nearly all the work: resolution (how many pixels per inch each page keeps) and JPEG quality (how aggressively each image is encoded). Dropping a 300 dpi scan to 150 dpi removes three quarters of the pixels while staying perfectly readable on screen. Converting to grayscale removes colour channels from documents that were never really in colour. Everything else is rounding error by comparison.
Sensible resolution targets
As a rule of thumb: 200 dpi and above is print quality, and worth keeping for anything that will be physically printed or archived. Around 150 dpi is comfortable for reading on screen at full zoom. Around 100 dpi is fine for reference copies and email. Below about 72 dpi, small print starts to soften noticeably. Choose based on what the document is for, not on the smallest number you can tolerate.
Hitting an exact size limit
Most upload forms do not ask for a quality level, they impose a hard limit — under 200 KB, under 1 MB. Working backwards from a limit by trial and error is tedious, which is why our compressor takes the target instead: enter the size you need, and it samples your own pages across a ladder of settings, projects the total, and builds at the highest quality that fits. If the result still exceeds the limit it steps down and rebuilds automatically.
When compression is the wrong tool
If your file is large because it has three hundred pages of real text, compression will barely help — split it instead, or delete the pages you do not need. If it is large because someone embedded a 20-megapixel photo, replacing that image is better than degrading every page. And if it is already been compressed once, squeezing it again mostly just adds artefacts. A good tool tells you when there is nothing worth doing.
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