pdfcosmos

Compress PDF

Shrink your PDFs by recompressing their structure (losslessly, with optional Fast Web View) in your browser.

Free, fast, and privacy-first.

Compress your PDF files

or drag & drop files here

PDF files onlyup to 30 filesup to 100 MB each300 MB total

Compress a PDF to a smaller size, losslessly and privately

A PDF that's too big to email or slow to upload usually carries redundant data and unoptimized streams. pdfcosmos recompresses that structure with qpdf to make the file smaller, losslessly, so your text and images are never touched and there's no visible quality loss. It all happens in your browser, so the document never leaves your device.

Add up to 30 PDFs at once, pick Standard or Maximum, and optionally turn on Fast Web View so large files start displaying before they've fully downloaded. If a PDF is already optimized (or is a scan made of images) it may shrink only a little, because qpdf doesn't downsample images. Either way you always get the smaller of the two files back.

  • Truly lossless

    Recompresses the PDF's structure and drops redundant data, so your text and images stay exactly as they were.

  • Never larger than the original

    If a file can't be made smaller you get it back unchanged, and the result shows exactly what was saved.

  • Nothing is uploaded

    Compression runs in your browser with WebAssembly. No file data is sent anywhere.

  • Optional Fast Web View

    Linearize a PDF so a viewer can show page one before the whole file downloads, handy on the web.

How to compress a PDF

  1. Add your PDF(s)

    Drop one file (or up to 30) into the upload area.

  2. Choose a compression level

    Pick Standard, or Maximum for a bit more (lossless structural) recompression. Optionally turn on Fast Web View to optimize the PDF for opening in a browser.

  3. Download

    Click the button. You'll see how much was saved, then download the smaller file (a ZIP for several).

Frequently asked questions

Are my PDF files uploaded to a server?
No. Compression runs entirely in your browser using WebAssembly (qpdf). Your files never leave your device. You can confirm it in your browser's Network tab: no file data is sent.
How much smaller will my PDF get?
It depends on the file. PDFs with uncompressed data, many redundant objects, or unoptimized streams can shrink noticeably. Files that are already optimized (and image-heavy scans) may shrink only a little, because this tool recompresses the PDF's structure and does not re-compress or downsample images.
Does compressing reduce quality?
Standard and Maximum are lossless: they recompress the PDF's structure and streams and drop redundant data, so your text and images are untouched. The Strong option is different. It re-encodes pages as images to shrink scans dramatically, which does reduce quality (see below).
What is Strong mode, and when should I use it?
Strong rasterizes each page and re-encodes it as a JPEG at a lower resolution, the only way to meaningfully shrink image-heavy scans in the browser. The trade-off is that pages become images, so the text is no longer selectable or searchable. Use it for scanned documents where Standard/Maximum barely help. Keep Standard/Maximum for text PDFs you want to stay selectable. You choose the image quality (Smaller, Balanced, or Clearer).
What if a file can't be made smaller?
You get the original back, unchanged. The tool never hands you a file that's larger than what you started with. The result shows exactly how much (if anything) was saved. (The one exception is Fast Web View: because it restructures the file, the result may be a touch larger than the original.)
What is Fast Web View?
Fast Web View (also called linearizing) reorders the PDF so a browser or online viewer can show the first page before the whole file has downloaded, handy for large PDFs hosted on a website. It doesn't change how the PDF looks or its content, and just optimizes the internal structure for streaming. It's optional and off by default.
Can I compress several PDFs at once?
Yes. Add up to 30 PDFs. One file downloads as a compressed PDF, and two or more download together as a single ZIP, each compressed with the same setting.
Is Compress PDF free?
Yes, it's completely free to use, with no sign-up and nothing to install.