The following script returns a page box and bleed box even if the PDF it is run on does not contain said boxes.
tell application id "com.adobe.Acrobat.Pro"
set trimSize to get trim box of page 1 of active doc
set bleedSize to get bleed box of page 1 of active doc
Is there a way to have Acrobat tell you if the page boxes are present or not in a PDF?