Hello there.
As far as I know. Yes, indeed, there is three things: manual/book and strategy guide, both PDF and a Read Me file as .TXT available. Further the options screen for game settings. Depending on the actual STEAM version.
AND I got a question:
Right at the start, after the helicopter crash...
where's the pilot and how to enter into the big gap (cave entrance) to the right.
The character is saying: 'I can't leave just yet.'
I got helicopter blade, medi kit, knife, camera, wire, computer, gloves, lighter, rope...
So the question is how to leave the helicopter crash side and how to enter the cave?
Friendly greetings.
April 2020.

post scriptum:
I got the game since yesterday, maybe you have already your answer. As I see it your question was a year ago. What a long time for becoming an answer on a imminent question.
As it is, it seems to be a good game.

Yes, I remember getting stuck temporarily. I don't have the game on me right now, but if you can't figure it out after another try then I will find the game and figure it out again!

To muscularrunner.
Hello, there.
I admit, without a notification, I forgot about this post.
Sorry, for the late (additional) answer.
Further, I found the way into the cave.
And later on to the Pterodactyl.

And depending to your question...
First:
The game manual (Steam version) is in the games main folder.
It can accessed from there with a adaptable editor.
Second:
Maybe take a look to the folders on your CD version.
If you are a bit lucky the manual is stored there, too.
I do not have the CD version, so I can not look for it.

Friendly greetings.
July 2020.

looks like it can be found on the replacementdocs.com site