I use Imagemagick for some things, but this is to recommend to other non technical users
A lot of people upload their sensitive files to online converters/compressors, and I’d like to recommend something easier
Say
- webp to PNG to jpeg
- compressing PDF, converting to and from other formats, extracting pages, unlocking, etc
for images, i use squoosh.app. it is a webapplication and not a desktop app. it can compress, convert & resize various image types. it is opensource and running offline (locally on your computer). github