I'm working offline, so this reply may be out of date, however - I should
not that v1.9 (beta code available in the public repo) allegedly supports
css etc; I haven't tried it, and since it isn't released yet you'd need to
compile it yourself, but...
Well, it comes as a console exe, but you can easily hide the window and
seamlessly integrate both input and output using stdin / stdout / stderr
streaming via the Process class in .Net. But it is coded as native C/C++,
not C#.
Other conversion software may be more suitable for your needs - but when I
last evaluated the various options (several years ago), HTMLDOC got my
recommendation for value, speed, low CPU impact, file size, options, etc...
And no, I don't work for them - just a happy customer.
Marc