Real conversion, not a renamed file
Changing a file extension does not change the format. Aimager fully decodes the pixels and re-encodes them with the destination format's encoder, then validates the magic bytes so you know the output is genuinely the format you asked for.
Choosing the right format
Use JPG for photos where small size matters and transparency is not needed. Use PNG for sharp graphics and transparency. Use WebP for the best all-round web format, and AVIF when you need maximum compression and your browser supports encoding it.