Your input is confusing - opening several files at onces and batch convertion are completely different tasks.
You can open multiple files by enabling "Add to the current document" option. Hundreds files is easier opening using Drag & Drop functionality on desktop - by selecting multiple files in file manager and dragging them into CAD Assistant window. In this case all files will be added to the single document, and saved file will contain all imported models too.
Batch conversion is currently not implemented. If this functionality is important for your project - you may send request through Open CASCADE contact form:
https://www.opencascade.com/contact