There is two version of Microsoft Rights Management, the AD RMS and Azure AD RMS, or called AADRMS, here is some tips to select which one fits you,
Minimum supported OS client
AD RMS: Windows XP
AADRMS: Windows 7
Minimum supported Office client
AD RMS: Microsoft Office 2007
AADRMS: Microsoft Office 2010
External trust
AD RMS: Domain RMS trust / Federation trust / Microsoft federation gateway
ADDRMS: Azure AD
License
AD RMS: RMS CAL
AADRMS: EA + RMS subscription
apart from the above differences, the two product has mostly the same features, including the PFILE format and RPFe folder support for non-MS Office type document, and the read only mobile client.
