How to use the compress pdf
- Drop a PDF onto the drop zone or click to choose one.
- Try "Optimise structure (lossless)" first. It keeps everything intact but savings are often small.
- For scans or image-heavy files, choose "Reduce image quality (lossy)", then pick a resolution (72, 110 or 150 dpi) and a JPEG quality.
- Click Compress, compare the before and after sizes, and download the result only if it is smaller.
Worked example
Choosing a mode
A text-based report exported from a word processor usually gains little from either mode, and the lossy mode can even make it larger. A 20-page scanned document saved at 300 dpi usually shrinks substantially with the lossy mode at 110 dpi and quality 70. The tool always shows the exact sizes and tells you when the original is already smaller.
How it works
Lossless: the document is re-saved with pdf-lib using compressed object streams, which packs the internal object table more tightly. Page content is not changed. Lossy: each page is rendered with PDF.js at dpi ÷ 72 times its size, encoded as a JPEG at your quality setting, and placed on a new page of the same size with pdf-lib.
Assumptions
- Lossy mode output is a PDF of page images. Text becomes part of the picture.
- Savings depend entirely on the file. No target size is promised.
Frequently asked questions
Are my files uploaded?
No. Your PDF is processed in your browser on your own device and is never sent to our server. You can disconnect from the internet after the page loads and the tool still works.
Why did my PDF not get smaller?
Many PDFs are already well compressed. The lossless mode only repacks internal structure, and the lossy mode can produce larger files for text-only documents because a page image holds more data than the text it replaces. When the output is not smaller, the tool tells you to keep the original.
What do I lose with the lossy mode?
Text is no longer selectable or searchable, links and form fields stop working, and fine detail gets softer. Use it for scans and photo-heavy documents where that does not matter, and keep your original.
Which resolution should I choose?
72 dpi is fine for on-screen reading, 110 dpi is a good balance, and 150 dpi keeps small text legible when printed at home.
Can I use a password protected PDF?
Not for editing. Encrypted or permission-restricted PDFs are refused, because editing them without decrypting would create a broken file or bypass restrictions set by the author. If you are allowed to, remove the protection in the software that created it first.
Limitations
- Files up to 100 MB are accepted, but very large or complex PDFs depend on your device memory and can be slow on phones.
- The lossless mode does not downsample images, so savings are often small or zero.
- The lossy mode removes selectable text, links, bookmarks and form fields.
- Encrypted or permission-restricted PDFs cannot be compressed.