You would need to purchase a Bentley Manual in the form released for sale to the public, then scan it for computer use.
If a legal proceeding were to make it before a Judge (this would be in the case of Bentley finding a "first source" PDF online, deemed downloaded enough to significantly effect sales), the fine for EACH download of that source PDF would be as follows.........
"the American Act requires the award of minimum damages
in the amount of $250.00 for each infringement, where actual damages are not proved."
http://scholarlycommons.law.wlu.edu/...&context=wlulr
That means each online download carries damages around DOUBLE the price of the Bentley Manual (paid by the person who produced the online PDF and allowed its download).
Sony was mentioned earlier as an example, and that's a VERY poor example. Seeing copyright holders act when sales are SIGNIFICANTLY effected. Sony is a multi-billion dollar company, Bentley a few million (the "time to act" trigger is a much lower number for Bentley).
And if you read the link, the court is not allowed to give ANY consideration to bankruptcy of the defendant, each 100 downloads would cost $25,000, plus court costs & lawyers fees/costs incurred. Again, no sane and/or smart person would consider an open PDF of the Bentley. Just because there's a lot of stupid in the internet, that's no reason to "join the pack".