Student or Learner
I know that 'free' can form 'freed' adding in this way 'ed'(with the meaning liberated,released).
So is this rule applied to all adjectives? I mean can all adjectives have a past participle form?
Verbs can have a past participle; adjectives cannot.
The past participle of many, but not all, transitive verbs can be used as an adjective, but some cannot. Of those that can be so used, some are not used directly before a noun. There are, unfortunately, no clear rules.