Although the perfective passive participial (having been Ved) of course contains a past participle within it, as distinct items they differ essentially in terms of privilege of occurrence.
A simple past participle can occur as a purely adnominal element, i.e. it can modify a noun phrase in the manner of an adjective. Thus we can say, e.g.
A man bitten by a viper may not have long to live.
in which 'bitten by a viper', here meaning 'who has been bitten...', functions as a modifying adjunct to NP 'a man' .
The perfective passive participial, on the other hand, serves in a manner that is rather closer to adverbial than adjectival. For instance, in the sentence
Having been bitten by a viper, the man immediately sought medical advice.
the boldfaced phrase actually means 'because he had been bitten...', and therefore serves to modify the VP, explaining why he performed the action in question, rather than the noun itself.
Occasionally, this functional distinction is expressed in terms of 'adjunctive' versus 'disjunctive' participials.
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