"Pro per" and "pro se" are both shortened Latin phrases meaning an individual acting as his or her own attorney in a lawsuit. Whatever the difference may have been to Ovid -- I never studied Latin -- there's no difference in court. It is simply a stylistic preference of the judge or lawyer or individual.
The "Does" represent persons as yet unknown by plaintiff who may be responsible for the wrongdoing alleged in the complaint. If you've been sued, you just answer or respond on behalf of yourself -- not the Does. Plaintiff may amend the complaint later to specify who the Does are.
Pro Se is usually used in federal court.
Pro Per is usually used in state court.
It means a party representing themselves.
My standard disclaimer: I am not offering legal advice, assume I do not know the law in your state and that I am just making suggestions for starting points for when you do speak with an attorney. Do NOT rely on anything I write and contact a lawyer in your area immediately after reading my posting.