Your file is processed on your device and is never sent to any server.
Shrink your PDF's file size on your own device. Best for scanned or image-heavy PDFs.
Large PDFs are almost always large because of embedded images, not text. CorePDFTools compresses by downsampling those images while leaving text and vector graphics untouched — so your text stays sharp and selectable. Everything runs in your browser.
Text in a PDF is stored as vector instructions, so it's already compact and stays crisp no matter how much you compress. The size lives in embedded images. A good compressor downsamples and re-encodes those images; it never rasterizes whole pages (which would blur text and often make the file bigger). This tool is best for scanned and image-heavy PDFs; a document that's already mostly text has little to compress.
Scans are the most compressible PDFs because every page is an image. Compression can cut their size dramatically while keeping them readable.
Documents full of high-resolution images compress well; downsampling those images is where the savings come from.
If a file is over your email provider's attachment limit, compressing the images usually brings it well under.
Three different ways to make a PDF smaller, and when each applies: Compressing images (this tool) is best when the file is large because of photos or scans. Removing pages with Split is best when you only need part of the document. Converting to grayscale before exporting helps when a colour scan won't shrink enough and colour isn't needed.
No. Only images are downsampled; text and vector graphics are left untouched and stay selectable.
If it's already mostly text, or its images are already efficiently stored, there's little to compress — so the tool returns your original unchanged.
No. Compression runs entirely in your browser; your file is never uploaded.
Start with Recommended. Use Light if image quality matters most, or Strong if you need the smallest possible file.
No. Compression changes how the content is stored, not the content itself — your pages and text remain.
Yes, in your mobile browser. Very large files may be slower due to a phone's limited memory.
No — image downsampling discards detail to save space. Keep your original if you may need full quality later.