Automatische Umwandlung von PES Dateien in PDF

Reader can't convert files. What happened, most likely, is that the PES file format got accidentally associated with Reader, although it can't open it. To solve it right-click one of the files (I assume you're on a Windows machine), select "Open With" - "Choose another app", then select the desired application and make sure to tick the box to use this application as the default handler for that file type, and press OK.