Attach a PDF to an event

Sometimes event participants should receive documents (before or after an event) that cannot be published on public internet.
It would be nice to have the possibility to upload those documents to alf.io event and then attach the document to emails sent to participants.

Note: I see a potential problem with attachment size, so I would limit it to max 2Mb
We should support PDF, could ZIP be an option to reduce the file size? or would that increase security risks?