I did my document in an ISO-standard. It does not support umlaut alphabets, such as ä and ö. I need them. The document gets compiled without UTF8, but not with UTF8. More precisely, the document does not get compiled with the line at the beginning of my main.tex:
\usepackage[utf8]{inputenc}
How can I compile my LaTeX document in UTF8?
Perhaps you should encode the letters using the appropriate latex formatting commands rather than changing the character encoding.
To accent letters with umlauts you want to use the command \"{o}.
Other accents are available, this site is a nice reference.
I'm not sure whether I got your problem but maybe it helps if you store the source using a UTF-8 encoding.
I'm also using \usepackage[utf8]{inputenc} in my LaTeX sources and by storing the files as UTF-8 files everything works just peachy.
Convert your document to utf8. LaTeX just reads your text as it is. If you want to use the utf8 input encoding, your document has to be encoded in utf8. This can usually be set by the editor. There is also the program iconv that is useful for converting files from iso encodings to utf.
In the end, you'll have to use an editor that is capable of supporting utf. (I have no idea about the status of utf support on windows, but any reasonable editor on linux should be fine).