You can't, nowadays everyone can copy-paste a well-written whitepaper from another project. You have to look at several factors like the idea behind the project, you need to check out that it isn't some money-grabbing vague idea with no substance. You also need to know if they're offering something innovative for the market, otherwise, you'll be investing in yet another project that offers nothing different from the 90% of the market.

There's also the communication aspect, do they communicate with people on a daily or weekly basis? Do they offer constant updates about the project? Do they engage in discussions about the project with the investors? and so on...

And those are just a few aspects about evaluating a project that you're looking to invest in, you shouldn't just look at the whitepaper, otherwise, you will fall for an ICO scam.