As Doug says, you can create an envelope from scratch. If you have an
envelope attached to a document, you should be able to print it by printing
page 0 or section 1, but if you want to remove the blank page, it can be
done.
1. With the insertion point in Section 1, go to Page Setup. Without changing
any settings, click OK (not Cancel).
2. Move the insertion point to Section 2 and press F4 (Repeat). This will
copy the Section 1 settings to Section 2.
3. In Normal view, select and delete the section break. Delete any empty
paragraphs that followed the section break. You should be left with just the
envelope.