[Wammertodging]

I wanted to load a book from my Kindle app on PC into Calibre for better reading, and I got the DRM tools as I've done this before, but for some reason when I load the book it converts it to Mobi and becomes illegible gibberish, everything gradually slants right with each page until the letters are on top of each other for pages at a time.

Does anyone have any ideas on what to do about this? I've been searching all over for two hours trying various things.