How to compress a PDF
Load the file, pick a compression level (recommended for everyday use, extreme when size matters more than sharpness) and click Compress PDF. You will see the original size, the new size and the reduction percentage.
Truly private compression
Other compressors boast about deleting your files "after one hour" from their servers. Here there is nothing to delete: the PDF is compressed by your own browser rendering engine and never travels over the internet.
How the reduction works
The tool redraws each page and re-encodes it as an optimized image, removing redundant data. That is why text in the resulting PDF is no longer selectable: it is the trade-off that enables large reductions while keeping the document readable and printable.