I agree with Bizi that doing this is betraying the trust of anyone you PM [unless the person asked for you to pass on the info or if a PM has multiple recipients/ CCs--when you message two or more at once you are implying that the subject of the PM can be shared by all the recipients (but no one else) on the PM that you sent out].

Also, PC Community guidelines say Community Guidelines (the list is longer than this but these are the ones that apply and they seem like good rules):

This is, first and foremost, a self-help support community. That means if your message (post or PM) isn't about offering support to another person or asking for it, it's potentially not appropriate for our community. Specifically prohibited from our community:
-Messages discussing a private message (PM) from others
-Members should generally not speak for, or about (especially in a negative manner), other current or past members. If a member wants to say something, they are welcomed to do so themselves. If a past member who's left on their own accord wants to say something, they're welcomed to start a new account.