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
my htaccess configs

These are real headers in browser inspector
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