squares and "???"

Hello

I'm sorry for my bad english, I will try to explain you with a picture, it's may be easiest ahah

I tried to find some answer about this problem but no solutions, it's quite hard to know "what/where/how"'

On my book I wrote some new pages, but the font was not available, it shows some ??????????? and squares, and I don't know a to get the original font of my page. Look :

I'm trying to change it since 2 hours, i abandon ahah Please help me !

Thank you for you answers !

Have a good day !

Regards

Jérome