My Word format for a normal 8 1/2 x 11 document has become corrupted. It opens with a document 16 inches wide instead of the normal 8 1/2 x 11. This happens with both a new blank document or an existing documant. If I change the right margin to 8 1/2, then the document doesn't print properly. What can I do to restire the default?

Evidently, you have done something to change the page size in Word's Normal template. Either:
1. Open Word's Normal template and re-set the page size; or,
2. If you have no other customizations/macros in Word's Normal template, exit Word, delete the template then re-start Word.

Word templates are normally stored in:
C:\Users\%Username%\AppData\Roaming\Microsoft\Temp lates\
File names end in .dot, .dotx or .dotm

To open a template for editing, select the 'All Word templates' option in Word's File|Open dialogue.

This won't affect any existing documents and it's not apparent how such a 'corruption' affecting a template could ripple through to your existing documents.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

Like Paul, I have no idea how anything other than a deliberate macro would be changing the size of existing documents.
A zoom setting could make something look very wide, but that would change the apparent size of text as well and would not show up on the ruler.

Below is a screenshot of the ruler for a document set for Tabloid (17x11) with narrow margins.

I recommend, if you need to fix the Normal Template, that you rename it rather than delete it. Many people have no idea of whether they have customizations stored there. Where is the Normal Template / How to Find the Normal Template

You may want to set your printer to one that will not handle paper that size. The screenshot was done setting the printer to Microsoft Print to PDF as the printer driver.
My physical printer would not accept that page size.