Second is after the letterhead and logo have been typed

In making a letter, it will usually always include the Letterhead as the identity of the institution or agency as well as the validity of the letter in addition to the signature and stamp.

The letterhead is at the top of the letter and is limited by a line from the contents of the letter. To make an underline on the letterhead, various ways can be done.

First is after the letterhead is made, then given a line using the command click ribbon insert then click shapes select lines (line). Using the mouse, click and hold under the letterhead then drag it to the margins while holding down the shift key on the keyboard.
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Second is after the letterhead and logo have been typed, place the cursor under the letterhead, then press the button on the keyboard:
--- (- at least 3 times) then press enter, to make a single horizontal line
=== (= minimum 3 times) then enter, to make a double horizontal line
### (# at least 3 times) then enter, to create a horizontal 3-fold line.
--- accompanied by pressing shift (- and shift at least 3 times) then enter, to make a single horizontal and thick line.
~~~ (at least 3 times) then enter, to make a horizontal wavy line
*** (at least 3 times) then enter, to make a thick horizontal dashed line.