Compress PDF Online — Free & Private

Compress PDF is for reducing large PDF files before email, upload portals, storage, or mobile sharing. It is not a cosmetic demo page: the compressor analyzes the file in your browser and applies different strategies depending on whether pages are image-heavy scans, text documents, forms, or mixed layouts.

What happens in the browser

The browser reads the PDF into memory, inspects page resources, and rebuilds a smaller copy. Image-heavy pages can be re-rendered at a controlled quality level while text-heavy pages are preserved so the words remain selectable. The goal is practical size reduction without pretending every document can shrink by the same percentage.

Step-by-step workflow

  1. Choose the PDF from your device or drop it onto the page.
  2. Pick a compression level based on the upload limit or email limit you need to meet.
  3. Run compression locally and wait for the size comparison.
  4. Open the preview if available and confirm text, signatures, and images are still readable.
  5. Download the smaller PDF and keep the original if you may need maximum quality later.

When this tool is useful

  • Sending invoices, statements, reports, and school forms under an email attachment limit.
  • Reducing scanned PDFs where photographs or page images dominate file size.
  • Preparing documents for portals with fixed limits such as 2 MB, 5 MB, 10 MB, or 20 MB.
  • Making mobile document sharing faster when the recipient has limited bandwidth.

Limitations to know before downloading

  • Mostly text-based PDFs may already be compact and will not shrink dramatically.
  • Strong compression can soften small print, signatures, or fine diagrams.
  • Password-protected PDFs should be unlocked first because encrypted streams cannot be optimized normally.

Privacy and file handling

The selected PDF is processed as a local browser file. The page uses client-side PDF libraries and Blob downloads rather than server uploads, so the document contents are not sent to PDF Compressor Unlimited for processing.

Compressing PDFs — what actually shrinks and what does not

Almost every PDF I have compressed in the last ten years fell into one of three buckets: scanned pages (huge, easy to shrink), image-heavy exports from InDesign or PowerPoint (medium, shrinks well), and text-only reports from Word or LaTeX (already small, almost nothing left to squeeze). Knowing which bucket you have tells you before you even hit the button whether to expect a 90% drop or a disappointing 4%.

Why some PDFs barely shrink

A 2 MB text-only PDF is already the compressed form of its contents. The fonts are subsetted, the text is FlateDecoded, and there is nothing left to throw away without corrupting characters. Do not be surprised when a 1.8 MB annual report drops to 1.7 MB — that is not the tool failing, that is physics. Real gains come from re-encoding embedded images at a lower DPI, which only helps when there are images to re-encode.

Real numbers from typical inputs

  • Phone-scanned 10-page contract, 48 MB → Medium quality: ~4 MB. Text stays crisp, signatures readable.
  • Marketing PDF with hero images, 22 MB → Medium: ~5 MB. Photos slightly softer, unnoticeable at screen size.
  • Word-exported report, 1.4 MB → Any setting: 1.3 MB. Do not bother.
  • InDesign brochure, 60 MB → High quality: ~18 MB; Medium: ~7 MB; Low: ~2 MB (visible softening on photos).

Which quality preset to pick

High re-encodes images at 200 DPI JPEG q85 — safe for anything that will be printed. Medium is 150 DPI q75, which is the sweet spot for email and web viewing. Low is 96 DPI q60 — use only when the recipient will read on a phone and you must be under 5 MB. Below Low the savings curve flattens fast and artefacts get obvious around text embedded inside images.

Step-by-step

  1. Drop the PDF onto the compressor. File size shows immediately.
  2. Pick a quality preset. Preview renders the first page at the new setting.
  3. If the preview looks fine, click compress. The estimated output size updates as pages process.
  4. Download. If the drop was less than 20% and you were expecting more, your PDF is text-heavy — no tool can help further without altering content.

Why browser compression sometimes loses to Adobe

Adobe Acrobat has one advantage a browser cannot match: access to Ghostscript-class object-stream rewriting that removes redundant fonts, deduplicates identical images, and rebuilds the xref table. In the browser we can re-encode images and strip metadata, but full object-stream rewriting is not viable in WebAssembly at reasonable speed. For 95% of consumer PDFs that gap does not matter; for a highly-optimised 200-page catalogue with repeated brand logos, Acrobat will beat us by 10–15%.