Best way to show each client his/her own private files


Hi, i’m new to ionic development.
This App will be very simple two part:

  1. Auth user without sign up
  2. Once user logged in he can see his/her own assigned documents.
    The first part is not a problem, but I would like someone with experience would advice me about the best way to obtain the second part goals.

I could create a string of the url in a firebase or parse database but
Where to store the pdf documents?