I work in Vegas Pro 8 but PI export that works is the same:
— Choose file type for export as .PNG,
— Create a folder in which the sequence will be made,
— Name particle sequence.
Once the Output Options window comes up:
— Choose desired length of sequence (the default number usually is the playback range you are using, so if you want shorter or longer, specify the “End frame”.
— Select “Save Alpha” and “Remove black from RGB channels,” hit “OK.”
NOTE: If you are rendering from within PI-3, you cannot have any window or program running over or covering PI or have it minimized for it will interrupt/stop the output render. On the other hand, the PI Render program can run in the background or minimized.