Compress PDF Online
Reduce PDF size for forms, portals, email, and document uploads with browser-local compression controls.
Written by Anil Gautam · Updated
Which compression mode should you choose?
Smaller scanned-style PDF is the default mode. Your browser renders every page with pdf.js, saves it as a JPEG picture at the quality you set and builds a new PDF from those pictures. Text becomes part of the image, so you can no longer select or search it, and links stop working. Use this mode for scans and photo-heavy files.
Clean PDF structure only rewrites the file with pdf-lib and packs its internal objects into compressed object streams. Images, fonts and text are left as they are, so text stays selectable and the saving is often small. Try it first on text documents that must stay searchable. The resolution and quality sliders are disabled in this mode.
How do resolution and image quality affect file size?
Resolution runs from 0.8x to 2.5x in steps of 0.1 and starts at 1.5x. At 1.0x a page is drawn at 72 pixels per inch of paper, so 1.5x gives 108 and 2.5x gives 180. Pixel count grows with the square of the setting, so halving the resolution leaves a quarter of the pixels. An A4 page becomes an 893 x 1263 pixel image at 1.5x and a 596 x 842 image at 1.0x, about 44 percent of the pixels.
Image quality runs from 35 to 95 percent and starts at 72. It is the JPEG setting: lower values discard more detail and leave smudges around small letters. After each run, zoom in on the smallest print in the downloaded file. If it is hard to read, raise the resolution and try a lower quality instead.
Why is the compressed PDF bigger than the original?
A PDF made of real text stores letters and font data, which take little space. Scanned-style mode replaces each page with a full-page image, so a short letter exported from a word processor can come out larger, and the size line then reads larger than original. Use Clean PDF structure only for such files. Each click on Compress PDF starts again from the file you loaded, so lowering the settings and compressing again does not stack quality losses. Every run downloads a new copy whose name ends in -compressed.pdf.
Sizes on screen count 1 KB as 1,024 bytes. If a portal's 200 KB limit means 200,000 bytes, a result shown as 199.0 KB (203,776 bytes) is still over, so aim for 195 KB or less on screen. Divide the limit by the page count to see each page's share: a 4-page form under 200 KB leaves about 50 KB per page. A file that needs a password to open stops with a 'No password given' message in scanned-style mode, and protected files can come out unreadable in the other mode, so remove any password first.