Well, I said in question that I installed SAP Crystal Reports for VS2010 and I can add a .rpt file to project; So why I should download Crystal viewr? that's not a good solution.
But I solve it just by following two steps:
1) In project Properties window in the Application tab changed the Target Framework from ".Net Framework 4.0 client profile" to ".Net Framework 4.0"
2) Added the CrystalDecisions.Windows.Forms reference to project
(in solution explorer right click in Reference folder and choose "Add Reference" --> for newbies such me)
Now I can add a crystalreportviewer to my project because after these two steps it appears in toolbox.
Without step 1 we can't do step 2 because When we want to add a Reference to project, the VS2010 filter the references and just show Target Framework references and allow to add them. CrystalDecisions.Windows.Forms is a part of ".Net Framework 4.0" not ".Net Framework 4.0 client profile"
It's so confusing...