How to print an envelope in OpenOffice.org?
The developers of OpenOffice have created a Wiki page where it's explained how the printing envelope procedure actually works. There is an in-depth guide on how to align, customize, add text, and basically modify every aspect of the envelope you add to the application. I recommend you browse to the page listed below to see exactly how it needs to be done.
Wiki Page/Envelope printing: https://wiki.openoffice.org/wiki/Documentation/OOoAuthors_User_Manual/Writer_Guide/Printing_envelopes