Compress PDF by Size — Free Online Compressor

Why are PDF files so large?

A PDF is really a container: text, images, fonts, and metadata all packed into one file. Three things bloat it. First, images — a single photo straight from a camera can be 5–10 MB, and PDFs often store it at full resolution even when it only ever displays at a fraction of that size. Second, fonts — when a PDF embeds entire font files so it renders identically everywhere, each font adds hundreds of kilobytes, and some documents embed a dozen. Third, inefficiency — many PDFs carry duplicate objects, leftover data from editing history, and uncompressed streams. A scanned 20-page document can easily pass 50 MB. The good news: most of this bulk is waste, and removing it is exactly what compression does.

How compression works on this page

When you drop a PDF into the tool above, it gets rebuilt from the inside out. The compressor parses every object in the file, then removes duplicates, strips unused data left over from editing, and rewrites object streams in compressed form. This structural rebuild works best on unoptimized PDFs — files saved by scanners or editors that never compressed their internal data. If your PDF is already well optimized, the tool will tell you so honestly rather than pretend to shrink it.

Honest limits: compression cannot shrink what is already compressed. A PDF whose images are already optimized JPEGs will barely shrink further. Scanned documents — which are really just big images of pages — compress less than text-based PDFs. And no compressor can recover quality that was never there. The output is always a trade-off between size and fidelity, which is why the tool keeps text perfectly sharp and only touches images.

When to compress — and when not to

Compress when you need to:

• Attach to email — most providers cap attachments at 20–25 MB, and oversized files bounce.
• Upload to portals — job applications, university admissions, and government forms often enforce strict file-size limits.
• Share drafts — sending a 4 MB version instead of 40 MB over chat or email saves everyone time.
• Archive — compressed files take less cloud storage and sync faster.

Do not compress:

• Print-ready files — if a designer or print shop asked for a press-quality PDF, compressing it can visibly degrade the printed output.
• Legal or archival originals — keep an untouched copy of anything where every pixel might matter later.

Make your PDFs smaller before uploading

• Scan at 150 DPI for screen reading — 300 DPI is for print; for documents read on screens, 150 DPI is plenty and roughly halves the size.
• Use grayscale for text-only scans — color triples file size with zero benefit for black-and-white documents.
• Delete blank or duplicate pages before compressing — every page costs bytes.
• Choose “smallest file size” or “web” presets when exporting from Word, InDesign, or your scanner software.
• Subset fonts instead of embedding full sets when your software offers the option.

Frequently asked questions

Will compression reduce the quality of my PDF?

Text stays perfectly sharp — it is never rasterized. Images may lose a small amount of detail at aggressive compression levels, but for screen viewing and everyday printing the difference is invisible. If you need pixel-perfect images, keep your original.

How much smaller will my file get?

It depends on what is inside. Text-heavy documents typically shrink 40–60%; image-heavy ones 60–80%. A PDF that is already well optimized may only shrink 5–10% — that means it was already in good shape, not that the tool failed.

Does it work on scanned PDFs?

Yes. Scanned pages are images, so they compress like images — expect moderate savings rather than dramatic ones. For the biggest reduction, rescan in grayscale at 150 DPI before uploading.

What happens to my file after compression?

Your document is processed securely and automatically deleted from the server a short time after you download the result. Still, as a general rule, avoid uploading documents you would not send by email.

Choose Your Target Size

Upload portals and email attachments often cap files at 1MB, 500KB, or even 100KB. Pick the “smallest file size” option — or a balanced setting for everyday sharing — and the compressor squeezes your PDF down while keeping text sharp. Pair with merge PDF first if you’re combining files before sending.

Smaller Files, Same Readability

Compression trims embedded image resolution and redundant data — the words stay crisp. Scanned PDFs shrink the most (often 70–90%), while text-based PDFs get modest but useful reductions. If images are the bulk, compress the images before building the PDF.

Frequently asked questions