Plaindre belong to the 3
rd group. Plaindre is a very common french verb.
Plaindre is conjugated the same way that verbs that end in :
-ndre
Plaindre is conjugated with
auxiliary avoir.
Plaindre verb is
direct transitive.
French verb plaindre can be conjugated in the reflexive form:
Se plaindre
Plaindre verb is a direct transitive verb, so passive voice can be used.