any suggestions on how to save a file without any encoding?
That question is meaningless; the "encoding" is the process of translating string characters to bytes to store/transfer (for example on disk). Any text content has to have an encoding. If you have saved it as UTF8, then the person reading it must also be reading it as UTF8. You could try including a BOM:
... new StreamWriter(path, false, new UTF8Encoding(true))
Alternatively, find out what encoding/code-page YOUR MACHINE is configured to use by default, and use that (it is Encoding.Default); for example:
... new StreamWriter(path, false, Encoding.Default)
If your user indicates that they need it in code-page 874 (aka "Thai"), then you would use:
... new StreamWriter(path, false, Encoding.GetEncoding(874))