Because need to read lot of things, in PDF, mobi and so on.
Do hope there could be TTS function.
Have you tried using Windows Narrator?
SumatraPeter is probably pointing you towards using narrator (or NVDA) for PDF, XPS, DjVu
It was available using the pre release version https://www.sumatrapdfreader.org/prerelease.html
I have not tried this recently perhaps you could report your findings with other formats for more info see
I am using Narrator, but it is not ok for Sumatra PDF reader.
Try it and you will see how it is.
I would like to have something like the TTS function in MoonReader on Android OS.