Why subjunctive?

[Aspulty]

I would like to know why the subjunctive is used in this sentence.

...No importaba el grado de convencimiento con el que se lo leyera...

[Rusty]

More context may be needed to give a complete answer, but this sounds like an opening clause, one that describes a speaker's perception of an impossibility. It's like a 'no matter what' or 'no matter how much' clause. Because it's an impossibility in the speaker's mind, the subjunctive is used.