Hello Matti!
Thank you for investigation. Unfortunately there is no way to set output encoding in Aspose.Words. There is a known issue in our defect database:
#1552 - Allow to set the encoding for HTML export in SaveOptions.
As a workaround you can re-encode the output before using it. .NET IO classes provide encoding selection. Basically you create two streams for input and output on the appropriate files and set output encoding. Then copy the file line-by-line. Also you can find a ready utility for that purpose or get right with that environment to avoid re-encoding at all.
Regards,
Viktor Sazhaev
Software Engineer,
Aspose Auckland Team