The following example demonstrates changing the font style in a TRichEdit component the following key combinations are pressed: Ctrl + B - Turns on and off Bold styling Ctrl + I - Turns on and off Italic styling Ctrl + S - Turns on and off Strikeout styling Ctrl + U - Turns on and off Underline styling Note: It is possible to set the font to include multiple styles.

Example:
const
  KEY_CTRL_B = 02;
  KEY_CTRL_I =  9;
  KEY_CTRL_S =  9;
  KEY_CTRL_U = 2 ;
procedure TForm .RichEdit KeyPress(Sender: TObject; var Key: Char);
begin
  case Ord(Key) of
    KEY_CTRL_B: begin
      Key := #0;
      if fsBold in (Sender as TRichEdit).SelAttributes.Style then
      (Sender as TRichEdit).SelAttributes.Style :=
        (Sender as TRichEdit).SelAttributes.Style - [fsBold] else
      (Sender as TRichEdit).SelAttributes.Style :=
        (Sender as TRichEdit).SelAttributes.Style + [fsBold];
    end;
    KEY_CTRL_I: begin
      Key := #0;
      if fsItalic in 
      (Sender as TRichEdit).SelAttributes.Style then
        (Sender as TRichEdit).SelAttributes.Style :=
        (Sender as TRichEdit).SelAttributes.Style - [fsItalic] 
      else
       (Sender as TRichEdit).SelAttributes.Style :=
       (Sender as TRichEdit).SelAttributes.Style + [fsItalic];
    end;
    KEY_CTRL_S: begin
       Key := #0;
      if fsStrikeout in 
      (Sender as TRichEdit).SelAttributes.Style then
        (Sender as TRichEdit).SelAttributes.Style :=
        (Sender as TRichEdit).SelAttributes.Style - [fsStrikeout] 
      else
        (Sender as TRichEdit).SelAttributes.Style :=
        (Sender as TRichEdit).SelAttributes.Style + [fsStrikeout];
    end;
    KEY_CTRL_U: begin
       Key := #0;
      if fsUnderline in 
      (Sender as TRichEdit).SelAttributes.Style then
        (Sender as TRichEdit).SelAttributes.Style :=
        (Sender as TRichEdit).SelAttributes.Style - [fsUnderline] 
      else
        (Sender as TRichEdit).SelAttributes.Style :=
        (Sender as TRichEdit).SelAttributes.Style + [fsUnderline];
    end;
  end;
end;