If the characters in the document are truly utf8 and not encoded in any other ansi codepage?
simply make your strings utf8 and maybe also add {$codepage utf8} on top of your source units. The latter is to interpret string literals in utf8 correctly.
Also note that if you are compiling for a terminal or console app, the codepage of te terminal must be utf8 too.
But the file may also have been encoded in a different code page, e.g. mid-european.
In that case, on Windows you sometimes need to use the provided conversion functions:
{$ifndef unix}
initialization
SetMultiByteConversionCodePage(CP_UTF8);
finalization
SetMultiByteConversionCodePage(CP_ACP);// system default
{$endif}