htaccess – How to prevent a specific PDF file from being indexed by search engines in WordPress?

In a wordpress multisite installation, I would like to block indexing of a specific pdf file using HTTP X-Robots-Tag response header using htaccess file.

Any of the indications found in previous related questions (i.e. this one) didn’t work in my case.

I used the instructions but all checks and every online checkers don’t shows the headers I’d need

These are my htaccess configs

These are real headers in browser inspector