When an answer provides a link to a document , website , etc. that includes a complete and exact treatment of the problem, but the answer itself has nothing in it's body (just the link), should I accept it? As an example , see this.
If the answer really is just a link: no, you shouldn't accept it. Answers are supposed to be self-contained, in that the content of the answer itself should be enough to answer the question without making you follow any links. (No matter how good the solution presented in the link, it is still behind a link, and is not part of the answer.) If you see a link-only answer, flag it as not an answer, and a moderator will convert it to a comment.
Of course, nobody is going to stop you from accepting a link only answer, or punish you if you do so. But if you care about keeping the site a good place to get questions answered, it's best not to encourage link-only answers.
Whether the example you linked to counts as a link-only answer is another issue. I suppose it is, technically, but it does include something beyond just the link. With an answer like that, it's probably best if the poster edits some of the content of the link into the answer. If the poster is unwilling to do so, then it could be converted to a comment.
It is up to you
which answer you want to accept. You are completely free and even encouraged to accept the answer that fits best your needs, helps you most, and you like best.
So if the link given in the answer makes you perfectly happy and perfectly fits your needs, just accept this answer ;-).
Of course, as David said it is generally better if answers explain a bit what can be found behind the link too, but it is not a prerequisit for an answer to get upvoted and accepted.