How to compress a PDF, step by step
Add the file, choose how aggressive the compression should be, and download the result. The important part is choosing the right level: 'strong' for email and web uploads, 'light' for anything destined for a printer, where losing image detail is visible on paper.
Compression targets exactly that overhead. It re-encodes the images at a sensible resolution for screen reading and removes duplicated resources, which is why the text of the document stays crisp while the file gets several times smaller.