You should look at OpenDocument for viewing reports. You can get the help documentation in the Developer Information section at http://help.sap.com/bobip. For Crystal Server 2013, look for the "BusinessObjects 4.1" section on the left. Crystal Server runs on the same platform as BusinessObjects, but it's limited to just processing Crystal reports.
The process you'll use is:
1. Create a login token using the regular platform SDK (either .NET or Java). This will also create an EnterpriseSession object.
2. Call OpenDocument using that token.
3. In the OnClose event handler for the window where the report is displayed, log off of the Enterprise Session that was created for getting the token.
-Dell