Add line over letter in Pages, Keynote In Cocoa programs in Mac OS it is possible, using the fonts palette, add line below the character (underline), in the middle of the character (strikethrough), changing the stile of the line: single, double, colour.

I need to add a line above a character (to represent antiparticles in particle physics). Is it possible to do without using drawing tools?

I need a line being possible to add above any character, not just ones that have lines in certain languages.
You can use Unicode combining character U+0305 COMBINING OVERLINE. It can be found by searching in the palette from Edit → Emoji &amp; Symbols (formerly Edit → Special Characters…), or by using a specialized keyboard layout such as the built-in Unicode Hex Input or my own custom one mostly designed for mathematics.

Here's some sample text with overlines, but note that the quality of the results may vary widely with the font, application, and operating system in use by the viewer.


  A̅ B̅ C̅ D̅ a̅ b̅ c̅ d̅ α̅ β̅ γ̅ δ̅ ε̅


Also, since the position of the overline depends on the height of the character, it will not necessarily align over multiple adjacent characters.

When using Unicode combining characters directly, you must type or paste them after the base character (and once you do so, they will be treated as one unit for editing purposes). This is the opposite of classic “dead key” combinations like Option-e a á where you specify the accent first.