Rephrase your question, it doesn't make sense.

While generating the Aged Trial Balance Report in the AR module, instead of directly opening the report, Sage directed it to be saved as a PDF in a file.

Confirm that your print destination is set to Preview.

My printer destination is in grey mode. I can't open to check into it. 
Thank you so much!

You need a "Change Print Destination" security right given from Administrative Services.