I am currently reading a PDF book, and in the text, there are strange jumblings of the letters like the ones in this screencap:
I don't think things like the collision between /t and /e can be explained by human error. A typist normally couldn't mess up the kerning that is in the font, and at other places in the text, the kerning seems to work. There is perhaps some technical issue that caused this. If you have encountered similar errors when typesetting books, please share what caused them and if it was something with the font or with some other software.