Saving a document in my folder as a type of web page,filtered

I have a web application that is suppose to save a document in my signature folder on my computer.
I need the file type/format to be in web page,filtered so that I can use that file in my outlook email signature.

the source code below is what I am using to save the file,kindly advise which file type/format should I use.

I have tried .htm and .html,however it seem not to be saving as web page,filtered.
Only when I manually open the rtf document and save as .web page,filtered - then it saves in a format that my signature is able to pick up.


What is strange is that,both ways of saving gives me a .htm file extension.