We do not know what you mean by "PFD", please do not use abbreviations. But the answer would be when the instructions for the "PFD" say it needs to be replaced.
Inflatable PFD
Every time it is worn!
A PFD for everyone aboard
a PFD for everyone aboard
a pfd for everyone aboard
According to the manufacturers instructions.
a pfd for everyone aboard
Wearing an inflatable PFD while on a personal watercraft.
In Florida it is against the law to operate a PWC with a restricted use type V inflatable PFD.
Life Jacket or PFD for everyone on board
any inflatable