Answer by Chenmunka for How to have full-width horizontal lines in Microsoft Word?

This is fairly simple:

1) From the ribbon, select Insert - Shapes - Line
2) Draw a line across the screen where you want it
3) Right-click on the line and select More Layout Options
4) Select the Text Wrapping tab
5) Select In Line With Text

You will now have a line across the document that will stay in place relative to the text around it.

You state in the question that Insert Shapes is hard for multiple lines. Not so if you select the In Line With Text option.
Note that the default is In Front of Text which is probably where you are finding the difficulty. This option does not move the line with the text as it is edited.