These DLL references need to be deleted and re-added, by right clicking on the "References" folder, and selecting "Add Reference...".
If this is an empty new C# project that you are writing, you'll need to add these DLLs in the same manner.
 
After selecting "Add Reference...", browse to the location where the SDK DLLs were installed. By default these are:
On a 64-bit machine:
if you installed the 64-bit MSI:
c:\Program Files\Microsoft\Trust Services Lab SDK and Shell (x64)\bin
if you installed the 32-bit MSI:
c:\Program Files (x86)\Microsoft\Trust Services Lab SDK and Shell (x86)\bin

On a 32-bit machine you have to install the 32-bit MSI, and the DLLs are located under:
c:\Program Files\Microsoft\Trust Services Lab SDK and Shell (x86)\bin

Currently, the Trust Services SDK is provided as 5 DLLs. Unless, you are familiar with which DLL has the functionality you require, we recommend you add references to all 5 DLLs (listed below) to your project:
Microsoft.SqlAzure.Trust.EdgeComplianceModule.dll
Microsoft.SqlAzure.Trust.SqlEdgeComplianceModule.dll
Microsoft.SqlAzure.Trust.TfsClientServerCommon.dll
Microsoft.SqlAzure.Trust.WcfFederation.dll
Security.Cryptography.dll