How can I be sure the PDF isn't uploaded?

Open your browser's DevTools (F12), go to the Network tab, and watch for requests while you use the tool. The only requests are this site's own script files (pdf-lib, PDF.js and its worker), which load when the tool first needs them; none of them carries your PDF. All processing happens in your browser tab.

Why compress a PDF without uploading?

Some files are not appropriate to send to a third-party service, and some networks block uploads altogether. This tool processes the PDF locally in your browser using pdf-lib. Our servers are not involved at any point.

Is there a file size limit?

Each PDF can be up to 100 MB. Larger files are rejected with a clear error before any processing starts.

Which quality setting preserves the most content?

Lossless mode restructures the PDF without changing any content. Text remains selectable, images are unmodified, and bookmarks are preserved. Image-based modes (High, Medium, Low) re-render pages as JPEGs, which reduces file size more aggressively but makes text non-selectable.

Compress PDF Without Uploading

Reduce your PDF file size entirely in your browser. All processing runs in your browser, with no third-party service or external storage involved. Choose lossless optimisation to keep all content intact, or pick a lower quality level for maximum file size reduction.

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How it works

Selecting a PDF only loads the bytes into the browser's memory through the File API. Lossless mode then asks pdf-lib to rewrite the document with object stream compression, while the image-based modes spin up pdfjs-dist to render pages to a Canvas and let pdf-lib embed the resulting JPEGs. Both pipelines complete inside this tab.

Processing runs in your browser

The entire pipeline runs in your browser, from selection to download. Our servers are not involved at any point. You can check this yourself in your browser's DevTools Network tab.

Related operations

To stitch multiple PDFs into one before compressing, try merge PDF. For pulling out a subset of pages, use split PDF. To extract pages as standalone images, see PDF to image.

Frequently asked questions

How can I be sure the PDF isn't uploaded?: Open your browser's DevTools (F12), go to the Network tab, and watch for requests while you use the tool. The only requests are this site's own script files (pdf-lib, PDF.js and its worker), which load when the tool first needs them; none of them carries your PDF. All processing happens in your browser tab.
Why compress a PDF without uploading?: Some files are not appropriate to send to a third-party service, and some networks block uploads altogether. This tool processes the PDF locally in your browser using pdf-lib. Our servers are not involved at any point.
Is there a file size limit?: Each PDF can be up to 100 MB. Larger files are rejected with a clear error before any processing starts.
Which quality setting preserves the most content?: Lossless mode restructures the PDF without changing any content. Text remains selectable, images are unmodified, and bookmarks are preserved. Image-based modes (High, Medium, Low) re-render pages as JPEGs, which reduces file size more aggressively but makes text non-selectable.

Last reviewed September 30, 2026

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