Updated September 2026
A PDF gets large for a handful of predictable reasons: oversized embedded images, a scanner that saved every page as an uncompressed bitmap, duplicated resources, or leftover metadata from whatever program exported it. Fixing the size means addressing whichever of those actually applies to your file — and the good news is you usually don't have to diagnose it yourself.
Drop your PDF into the compressor above and it runs both of the techniques described below automatically, keeping whichever result is smaller. No settings to choose, no guessing whether your file is "the scanned kind" or "the export kind" — the tool tries both and picks the winner. See exactly what runs on the How It Works page.
PDFs accumulate redundancy — the same embedded font subset referenced on every page, images stored less efficiently than they need to be, objects duplicated by whatever tool generated the file. Recompressing images in place, recompressing fonts, and deduplicating repeated objects can shrink a file noticeably without changing how a single page looks or reads. This is close to a free win: text stays exactly as sharp, and it stays selectable.
For image-heavy PDFs — scanned documents especially — the bigger win comes from re-rendering each page at a more reasonable resolution and re-encoding it with efficient JPEG compression. A scanner set to a high DPI can produce pages several megabytes each; re-rendering at a resolution suited for screen reading and normal printing (this tool uses 150 DPI) often cuts that by 50–90% with no visible difference on a screen or a standard printout.
Desktop PDF editors often ask you to manually pick an image-quality slider, choose a target DPI, or decide whether to "downsample" images — decisions that are easy to get wrong in either direction (too aggressive and text-adjacent images blur; too conservative and the file barely shrinks). Because this tool tries the higher-fidelity structural pass first and only falls back to re-rendering when it actually wins, you get a reasonable result without needing to understand DPI or JPEG quality settings at all.
Occasionally a PDF is large because of what's genuinely in it — dozens of full-resolution photographs embedded for a reason, for instance — and no compression pass gets it dramatically smaller without a visible quality trade-off. In that case: consider splitting the document into smaller parts (a scanned book by chapter, an invoice batch by month), or check whether you actually need every embedded asset at its original resolution. For emailing specifically, see compressing a PDF for email, which covers typical attachment limits and what to do when compression alone isn't enough.
After compressing, the tool shows the original size next to the new size and the percentage saved — worth glancing at before you rely on the result. A large percentage on a scanned document is expected and a good sign; a 0% or near-0% result on a file you expected to shrink usually means the PDF was already efficiently built (a well-exported report, for instance) rather than a sign something went wrong.
If you've used a desktop PDF editor before, you may have hit a menu asking you to choose a compression "level" (low/medium/high) without much explanation of what each level actually changes. That framing assumes you already know whether your file needs lossless cleanup or a heavier image re-render — most people don't, and picking wrong either wastes the opportunity to shrink further or degrades a file that didn't need it. Running both techniques and keeping the smaller, validated result removes that guess entirely.
Will this always make my PDF smaller? If there's genuinely nothing left to compress, you'll get your original file back unchanged rather than a larger "compressed" version — the tool never hands back something bigger than what you started with.
Do I need to know anything about DPI or image quality to use this? No — the tool tries the available techniques and keeps whichever result is smaller automatically.
Is there a limit to how many times I can compress a file? No — compressing a single PDF is free and unlimited. Compressing several at once as a batch ZIP is a one-time paid feature; see the batch guide.