Hi,
Thanks for contacting us, for the rules reminder too, Samuel. This is the case of all the WordPress plugins that make an integration with a paid webservice that include a trial version.
Regarding the commercial part, you can find some free plugin here that apply a compression on image (not on PDF). The existing free plugins include: an optimization done on your server that take a lot of resources, especially for PDF + usually a less advanced algorithm that compress around 10-15% the media.
We’ve write in bold in the description: “Test full service for free during 15 days.” and I’m sorry if you feel disappointed.
Cheers,