An integrated spelling engine checks the text as you type within Rich Text controls. When checking words, the speller engine references common English dictionaries. The user can also add new words as required, as well as choose the dictionary to use.
A range of auto-correct options are also available. To examine the spelling checker options look under Tools > Options > Spelling Options... menu.
Adding words to your dictionary will update the dictionary file in your windows documents and settings folder. If you change your login or move to another computer, you will be accessing a different dictionary which will not contain your custom words.
You can take your dictionary with you if you need to change computers. Your dictionary is located at C:\Users\[User Name]\AppData\ and is called [User Name].adu