Personal pronouns are pronouns that are associated primarily with a particular grammatical person – first person (as I), second person (as you), or third person (as he, she, it, they). Personal pronouns may also take different forms depending on number (usually singular or plural), grammatical or natural gender, case, and formality. The term "personal" is used here purely to signify the grammatical sense; personal pronouns are not limited to people and can also refer to animals and objects (as the English personal pronoun it usually does).
The re-use in some languages of one personal pronoun to indicate a second personal pronoun with formality or social distance – commonly a second person plural to signify second person singular formal – is known as the T–V distinction, from the Latin pronouns tu and vos. Examples are the majestic plural in English and the use of vous in place of tu in French.
For specific details of the personal pronouns used in the English language, see English personal pronouns.
Pronoun is a category of words. A pro-form is a type of function word or expression that stands in for (expresses the same content as) another word, phrase, clause or sentence where the meaning is recoverable from the context. Pronouns mostly function as pro-forms, but there are pronouns that are not pro-forms and pro-forms that are not pronouns.[p. 239]
It's a good idea. (pronoun and pro-form)
It's raining. (pronoun but not pro-form)
I asked her to help, and she did so right away. (pro-form but not pronoun)
In [1], the pronoun it "stands in" for whatever was mentioned and is a good idea. In [2], the pronoun it doesn't stand in for anything. No other word can function there with the same meaning; we don't say "the sky is raining" or "the weather is raining". So, it is a pronoun but not a pro-form. Finally, in [3], did so is a verb phrase, not a pronoun, but it is a pro-form standing for "help".