Upvote:3
Even if you do not read Russian, I suggest you use google translate (or a similar program) to read the Russian Wikipedia page regarding the document; there you will also find a part of the handwritten version of the letter signed by Lenin: https://ru.wikipedia.org/wiki/%D0%9F%D0%B8%D1%81%D1%8C%D0%BC%D0%BE_%D0%BA_%D1%81%D1%8A%D0%B5%D0%B7%D0%B4%D1%83
This should resolve quite a few questions you have. Among other things, the authenticity of the letter was not disputed by the participants of the 13th communist party congress it was written for. (But, of course, Kotkin knows better :)) In response to the letter, Stalin offered to resign. The letter was declared to be a forgery after Stalin defeated the opposition.