As the article stated, in this specific case the bank used an "invisible" character (a minus sign) to assist in alignment .. which resulted in errors when parsing the text nodes by layout.

OCR of a digital image generated from those PDF draw commands only operates on the visible portions that are rendered.

Another case to be considered .. FOI requests for documents from "pain in the arse" government departments or law firms can result in "digital documents" that are deliberately generated to be difficult to process (go figure) .. eg: filled with circular and spaghetti draw commands that "print correctly" but are a nightmare horror show to parse.

( "technically compliant" is a legally compliant "fuck you" )