The Bitcoin Whitepaper
This is the most important document of them all. Whether you’re a newcomer trying to get a grasp on the concept or a seasoned verteran. This is where you start and this is where you come back to when you loose perspective.
For posterity’s sake the Bitcoin whitepaper has also been uploaded to the blockchain. You can find the pdf in the following transaction: 54e48e5f5c656b26c3bca14a8c95aa583d07ebe84dde3b7dd4a78f4e4186e713 (source)
Blockchair.com also has a nice service verifying the most popular hosting of the bitcoin.pdf file. Making sure they are hosting the original file.