"I forbid it."
Yes, as a personal pronoun, when it is the subject. If you say "Απαγορεύω αυτό", it's "I forbid this", in which case it is a demonstrative pronoun. See also troll's comment here; it's currently the last comment. More on strong and weak pronoun forms here or if you search for 'strong AND weak AND pronoun' in the Greek discussion forum.
https://en.wiktionary.org/wiki/%CE%B5%CE%B3%CF%8E#Related_terms is one place to look (you may need to open up the table "Personal and possessive pronouns" first before you can see it).