How to Compress a PDF
Shrink a PDF for email or upload — without uploading it anywhere.
Email limits, upload forms, and messaging apps all reject PDFs that are too large. Compressing the file is the fix, and on ToolHamper it happens entirely in your browser: the Compress PDF tool reads and rebuilds the file on your own device, so nothing is ever sent to a server. This guide explains how to get a genuinely smaller file without ruining the pages.
What actually makes a PDF big?
Almost always, it is the images. A scanned document or a brochure full of photos stores those pictures inside the PDF, often at a much higher resolution than anyone needs on screen. Plain text, by contrast, is tiny — a text-only PDF is already small and will barely shrink. That is why compression works by re-compressing the embedded images, and why a photo-heavy PDF can shrink dramatically while a text-only one hardly changes.
Step by step
- Open the tool. Go to Compress PDF and click the upload box, or drag your PDF onto it. The file is read locally by your browser — it is never uploaded anywhere.
- Choose a quality level. Pick one of the three levels. Lower quality compresses the images more aggressively and gives a smaller file. Higher quality keeps images sharper but saves less space.
- Compress. Press the compress button and give it a few seconds. The tool rebuilds the PDF in your browser's memory.
- Compare the sizes. The tool shows the before-and-after file sizes honestly. If the saving is tiny, your PDF was probably already well optimized — that is a result, not a failure.
- Download and inspect. Download the compressed PDF and open it. Check a few pages, especially ones with photos, and make sure the quality is still good enough for your purpose.
Choosing the right quality level
Work backwards from where the file is going. For an email attachment or an online form, the middle level is the sensible default: a large saving with images that still look clean on screen. Choose the highest quality when the document will be printed or read closely, and the lowest when every kilobyte matters — for example, a strict upload limit — and the pages are mostly read on phones. If the result is not right, go back and try a different level; because everything runs locally, re-compressing costs you nothing but a few seconds.
If the file does not shrink
A text-only or already-optimized PDF cannot shrink much — there is nothing wasteful to remove. In that case, consider whether you need the whole document: Split PDF can extract just the pages you need, and a few pages are always smaller than the full file. Password-protected PDFs cannot be opened by the tool at all; remove the password with the app that created the file first.