Are you saying the XML you have (the source) does not specify an Encoding Type ?
Have you tried examining the Encoding Type of the XmlDocument your source is (hopefully) read into using : XmlDeclaration.Encoding get/set Property: what happens if you do ?
If your source XML is .NET generated, and does not specify an encoding attribute: UTF-8 will be the default in either reading or writing out the XML.
Assuming you have read in the XML using 'StringReader or whatever, and you have a valid 'XmlDocument created, when writing it out, as UTF-8, you should create an XmlDeclaration instance, set the XmlEncoding property of that instance, and add it to the root node of the XmlDocument.
This is shown in the code example here on MSDN:[^
Now if your source XML is in some weird format, that you don't know, and can't determine: perhaps that mean you are going to have to figure out its structure yourself and use an XSLT to get into a usable form ?
good luck, Bill