Here is the quickest way to get that PDF file.
The easiest way to "télécharger" your proof of travel is through the official Île-de-France Mobilités (IDFM) website or mobile app. Log in to your IDFM Connect account. Navigate to the "Mon Navigo" (My Navigo) section. Select your specific pass (Annual, Imagine R, etc.).
Have you successfully gotten your employer to reimburse your Navigo? Let us know in the comments below!