RTA files exist as 2 different types. Please find information about each of them below.
Type 1: RoboHelp RTA Data File
The rta file extension is associated with two file types. The most common is the RoboHelp RTA Data File format by Adobe Systems. These files are used internally by the RoboHelp software. RTA files are...
The rta file extension is associated with two file types. The most common is the RoboHelp RTA Data File format by Adobe Systems. These files are used internally by the RoboHelp software. RTA files are not meant to be opened manually. The rta extension can also be used by IBM ViaVoice speech recognition software. It contains saved language dictionaries. This type is likely obsolete now. In general, rta files are considered data files. But they may also contain audio. The rta extension is supported by Windows and Mac. It can be found on both desktops and mobiles. Rta files have a low popularity rating. So they are not very common for average users.
Adobe RoboHelp
TrueRTA