See, according to the former Assistant U.S. Ambassador in Haiti, Luis Moreno, it’s not that hard to get a president to sign a resignation letter. You tell him what to write, and well, aside from threatening to slaughter a few hundred or maybe thousand citizens unless he signs it, you don’t really have to do all that much. Then you go on to dictate your version to the stenographers at the Washington Post and repeat it to any bothersome U.S. citizens who show up at the embassy later to ask questions, shrugging your shoulders about the surprising nature of it all and pretending to be completely perplexed about it.
You should of course, have all this happen on the way to the airport, preferably in the middle of the night. Typing a letter and dating it the THURSDAY before the forced rendition is clumsy, and will only add to suspicions that the letter is faked, which of course the kidnapped president is going to claim, when a letter magically turns up three days later with his three letter nickname forged upon it.
There is a much better view of the letter available here.