Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

procedure ConvertFile(const FileName: string; fromCodepage: Integer);
 var
   ms: TMemoryStream;
 begin
   if getOEMCP <> fromCodepage then
     raise Exception.Create('ConvertFile: Codepage doesn''t match!');
   ms := TMemoryStream.Create;
   try
     ms.LoadFromFile(FileName);
     // make backup 
    ms.Position := 0;
     ms.SaveToFile(ChangeFileExt(FileName, '.BAK'));
     // convert text 
    OEMToCharBuff(ms.Memory, ms.Memory, ms.Size);
     // save back to original file 
    ms.Position := 0;
     ms.SaveToFile(FileName);
   finally
     ms.Free;
   end;
 end;