texte d'un PDF non reconnu dans illustrator

It's a PDF. You get what you get.

You can try and turn on "Missing glyph protection"

If you don't plan to edit the text, you can place the PDF into a new file (linked), then Object > Flatten transparency (check outline text)

You may simply need to install the respective font on the system. This is quite common for construction plans since the CAD programs usually do not embed full font sets or use custom solutions not based on fonts to create labels according to ISO/ DIN standards or whatever compliance is required and thus AI has nothing to extract or re-create.

Mylenium