permissions – Opening a file of the theme from outside

I have a problem.
I want to open a file that is in the active theme. Actually, I have a link that is shown in an admin menu, and when I click the link I want to redirect to a file that is stored in the theme folder, but I am getting a http 500 error. Is there any chance that the file don’t have permission to open from the admin pannel?

The menu in the admin pannel looks like this:
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When I click the pdf icon(at the end of each row in the table), I want to redirect the the file placed as in the photo below:
enter image description here

The file actually contains code for generating a pdf(with tcpdf plugin).
The value of the href attribute of the link to redirect to the file is :
enter image description here

After clicking the link, is shown the error below:
enter image description here

Any idea where can be the problem ?