Hi Antoine,
Please read this documentation:
edocmandocs.ext4joomla.com/getting-started/edocman_acl
, this documentation shows you about the ACL setting of Edocman extension.
You'll see 2 options: Edit and Edit Own. Here you can select Denied with 2 permissions on Registered group. By this way, user won't able to edit documents at front-end
Thanks
Dam