Interacting with Desktop Files such as .pdf documents

Hello all, first time poster here. I've been learning mojo for about a month and I'm having an issue trying to open a .pdf file using just Mojo, no Python (likely not supported at this time?) following this guide: https://docs.modular.com/mojo/stdlib/builtin/file/

Am I missing something here or is reading content from a .pdf file not possible a this time?