Yes, the DtsConfig file contains parameters for the SSIS package - it is one way of making the package more flexible by changing parameters instead of rebuilding the SSIS package every time you want to change a value.
There are several ways to open the the actual SSIS package (the dtsx file).
One way is to open Visual Studio, create a new SSIS project and then, in the Solutions Explorer, right-click on 'SSIS Packages' and select 'Add Existing Package'. from this dialog you can select the Server and then the package you want to import.
You can also connect to the Integration Services Server via SSMS, right click on the package under 'Stored packages/MSDB' to locate your SSIS package. then right-click on it and select 'Export Package...' to save it as a file or even move it to another IS Server.
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