Non riesco più a selezionare i pdf su anteprima

Select what, exactly? Can you post screenshots showing the problem?

Trying to guess what you are seeing... I wonder if you are trying to select TEXT in a pdf.

Some pdfs may contain text, but others may contain an image of text - e.g. from a scanner. In the latter case you cannot select any text.

Maybe that is your problem

Hi vinichenov,

Thank you for using the Apple Support Communities. You've posted a question in the English Community. If you are able to repost your question in English, you may reach a larger audience and have a better chance of receiving a reply.

Thanks!

Could you tell us, for the benefit of other users, what the problem was and how it was solved?