The option to add on .rdp file to redirect only selected drive (the default is every) is:
This redirect only drive C:
If you are working with Windows 2012 R2 Remote App, you should use powershell to add the required custom properties:
Set-RDSessionCollectionConfiguration –CollectionName MyCollection -CustomRdpProperty “drivestoredirect:s:C:”
If you are using Windows 7 as client, remember to update “Remote Desktop Client” (mstsc) otherwise selected redirection is not working.