I’m sorry I’m going to be late with this one as I do not have Armenian letters(I use translit usually with friends/family). I will get them once I get to Armenia(June 4th) and translate the invitation then!
You can try the Google Input Tools, they have an on-screen keyboard so you can look up the letters while typing, or even type with the mouse (but that would be slower). I hoped they have transliterated input with word suggestions in Armenian letters as well, but that they only have for other languages (like, fortunately, Nepali for our other Future Makers project)
Thanks @Matthias I was also thinking about this! Will try typing here till i get home, as it will also help me remember and locate the Armenian letters on my keyboard