Copy & Paste is possible in this client. This combined with task-switching to your desktop is a great way to save and re-post large letters, articles, and essays in the in-game libraries, mail, and appropriate bulletin boards.

Note: Do not be fooled by what may be seem like an impersonation of another character. It is possible to copy multiple lines.

For example, if the following lines are copied and pasted it would seem like the second character had said the lines:

CharacterA: multiple lines copy&pasted...
CharacterB: blah blah

It seems that CharacterB said "blah blah", but it was several lines copied and pasted by CharacterA.

Be wary of this in conversation and when viewing screenshots.