Here are seven signs of paranoid personality disorder in others. If you observe them, be aware, that pointing it out to them is not actually a good way to solve the problem; treatment is hard, and they're extremely likely to feel threatened by anybody who says there's something "wrong". Ultimately, knowing a person with PPD is hard, and will likely take a toll on you.

1. They Read Negativity Into Every Interaction: The key diagnosis of paranoia isn't necessarily that the person believes in conspiracy theories and invests in a tinfoil hat. It's the presence of inherent suspicion about the motives of others, even if it's completely unfounded; and that can express itself in a lot of ways, including taking innocent remarks as threats, interpreting impersonal social interactions as slights, and generally distorting all other people as likely to hurt them. 

2. They Are Highly Suspicious Of All Authority Figures: Their paranoia usually doesn't extend to believing that inanimate objects are "out to get them" (that's a feature of delusions, which don't usually figure in PPD); but if they're dealing with a big organization, like a bank or the government, or people with superiority (like bosses), they're likely to believe, without any justification, that they're working to potentially hurt them and will use their power for ill

3. They're Intensely Jealous: Interpersonal relationships with people with PPD are, understandably, difficult, because a person who can't look at other people without being inclined to believe the worst about their intentions is a fundamentally distrusting partner. Their distorted world view indicates that, even if somebody insists they're loving and faithful, the possibility of betrayal is extremely real and very likely.

4. They're Secretive And Can Isolate Themselves: This is an unsurprising consequence of the condition that makes their interactions with other people deeply threatening:  They will withdraw from social interactions, be difficult to draw out of their "shell," and regard all attempts to entertain or cajole them as suspiciously motivated. Expect hostility if they refuse to come out and you try to persuade them.

5. They're Seriously Aggressive & Defensive: Don't underestimate the power of the distortion of PPD; even if it makes no sense, they will defend their suspicions to the point of fights. those conversations can go wrong: they might keep getting distracted by anger at their perceived slight.

6. They're Hard To Collaborate With: Interesting contradiction in PPD sufferers: while you may decide you want them on your team because they "appear to be objective, rational, and unemotional," their disorder means that their responses will actually be deeply divisive when it comes to group work, whether it's a project at work or organizing a birthday party. 

 7. They Could Hold Grudges For Their Country: The PPD sufferer is not in a condition in which any perceived slights or problems with others are easily let go; instead, they brood on them and will hold suspicions about the person and their motivations for the remainder of their time with them. 

The devastating thing about PPD is that one of its central tenets is the belief that the sufferer's paranoia is correct and that other people are not to be trusted, which makes their seeking help both unlikely and highly difficult to achieve. Building a bond with a therapist or doctor is, as Psychology Today explains, very tricky, particularly if they recommend medication; it's very likely that PPD sufferers will walk out of psychotherapy sessions prematurely.