Student or Learner
In the next sentence:
Is that sentence in passive form??
because I've undestood that in the passive form is not necesary to use personal pronouns.
Thanks for the help
No, the sentence is not in the passive voice. Although finding a conjugation of "to be" (which "am" is) in a sentence is a clue to passive voice, it is not conclusive. Finding a "to be" with an -ed word is a better clue to passive ("It is hoped you understand this").
A passive construction occurs when you make the object of an action into the subject of a sentence.("Why is the road crossed by the chicken?")
In your sentence ("I'm interested.") there is no object. The one doing the action (that of being interested) is "I" and "I" is at the normal subject position (first) in the sentence, so it's normal active voice.
I do not understand what you are saying about "in the passive form is not necesary to use personal pronouns." Perhaps someone else can illustrate that, if it is true.