How can the pharmacy's debt be paid without informing its owner, in order to avoid being accused of theft and the problems of a bad reputation?

You are absolved of this right by returning it to its owner by any means, and you are not required to inform him of the truth of the matter; rather, concealing it is preferable. It suffices to tell him: "This money is from someone who wronged you," without specifying the person. For whoever repents to Allah must return the grievances to their rightful owners. If one fears exposure, he can resort to stratagem by sending the money or its equivalent to its owner with a message stating: "This is for you from someone who wronged you in it and has repented to Allah."