Can I terminate ah HVAC condensate drain line through a soffit?
An A/C system in an attic usually has two condensate lines. One is the Primary line. The other is a Secondary line. The primary is usually ran to a main plumbing drain. The secondary line is ran to a Conspicuous spot. A spot that is EASILY seen. If the Main line plugs up, then the "overflow" secondary line will start to drip. this is to let the homeowner know there might be an issue with the the condensate or with the coil itself. If this is the case I would have a Tech come take a look at the system. 

The secondary line is a safety device to help keep condensate liquid from leaking into the structure of the home. 

Hope this helps.