Been looking for that one myself after a documentary mentioned it. Honestly, it's surprisingly elusive for a book that's had such cultural impact. The most reliable path I found was checking the usual ebook retailers—Amazon Kindle, Apple Books, Kobo. It's often available for purchase there as an ebook. Sometimes you can find a PDF floating around on academic sites or author-focused forums, but those are hit or miss and the quality's not guaranteed.
Your local library's digital service, like Libby or OverDrive, is a solid bet if you're willing to wait. I had to place a hold for the digital copy. It's not the kind of title that's just free on some big aggregate site, which makes sense given its niche. The search kinda feels like part of the process for a book about, well, intermediaries.