The RTF format is very widespread and you can edit it in many ways. Just as an apple doesn't say much about the species, neither does the term "RTFEditor". The plus key is available via the combination shift =, via the numeric keyboard and can also be obtained via the ALT 43 key combination. The + key may have been used or reserved for a special function in your editor. Or does your favorite support a programmable key function or a macro in which you can use the ALT 43 combination.