It's more like you can plead not guilty but still be convicted. So by accepting the pardon you are admitting you are in fact guilty. Kinda fucked in other situations really.

Yes by judicial precedent. Quoting Wikipedia's article on federal pardons in the United States: According to Associate Justice Joseph McKenna, writing the majority opinion in the U.S. Supreme Court case Burdick v. United States, a pardon is "an imputation of guilt and acceptance of a confession of it."

A pardon issued and accepted (United States v. Wilson set the precedent that a pardon may be rejected by the intended recipient) does not erase an indictment or conviction. Pardoning a convict ends any prison sentence, fine or other punishment but does not erase felon status. For that you need an expungement.

Note: One does not need to be convicted for the president to issue a pardon. A pardon can end a trial before it begins.

Accepting a pardon does permanently satisfy one's fifth amendment right against self-incrimination. In that way it's kind of like pleading guilty and being sentenced to reading this piece of paper from the White House. You can't be tried and punished for this same crime, which means you CAN be compelled to testify about it.

Because you automatically admit guilt when you take a pardon. Please whatever you want, taking a pardon makes you instantly guilty of the crime regardless.

You can also no longer plead the 5th, you MUST answer questions regarding your crimes and the crimes of others.

Depends on your job, any gov job is now an auto-disqualifying him for having a felony. International travel is also a lot harder now if he has a felony.