When composing a letter in an external word processor, it's best to save the content as plain text without line breaks before pasting it into a Web form textbox.
To save a document as plain text in Microsoft Word:
The procedure is similar for other word processors.
While "Smart" (aka "curly") quotes usually pose no problem, it can result in mis-interpreted characters when pasted by some Mac users. Therefore, and given their limited utility, all users are recommended to turn smart quotes off.
To turn off curly (aka "smart") quotes in MS Word:
Follow Tools-->AutoCorrect-->AutoFormat As You Type and deselect the box titled "Straight Quotes with Smart Quotes."
-AND-
Follow Tools-->AutoCorrect-->AutoFormat and deselect the box with the same heading, "Straight Quotes with Smart Quotes."