MS Word auto formats entire document with EVERY change

[rooter]

For years I have gritted my teeth and screamed and googled but have still never figured out how to change my settings or documents from the ENTIRE document changing each time I do any formatting in line or from selecting a line.
For example, I'm mid typing within a document and choose command b for Bold and the ENTIRE document from the beginning becomes bold.
If I select a word within the document and choose bold or with the mouse tap a new color, then ENTIRE document becomes bold or the new color.
If I select increase indent, the ENTIRE document changes.

It makes no difference if I use the mouse and select formatting on the menu or if I use shortcut key commands. It's not about selecting the return character, I can select with and without the return character and the same thing happens. I can be in a table and change something and the ENTIRE document changes still (within and outside of the table)

I have checked my preferences a hundred times, I have done everything I can imagine, but I can not change it.....
However, sometimes if I open a file that I receive from someone else (ie email or download) that file does not do this. I have sometimes taken those documents and deleted all info and save it to open as a new blank document... but honestly I'm afraid to change settings and it takes much longer to do. Besides the fact that it's ridiculous to have to do.

Usually if I hit undo once it will undo the entire document formatting and keep only what I was trying to adjust, but not always. And if I don't notice right away, the entire document is messed up.

I am on a MacBook Pro, Have MS Office for Mac 2011 with all current updates. I am running OS X 10.6.8 but have had this problem I have had this problem for years (so several OS's)... I have wanted to kill forever but am always tight on deadlines or have simply given up trying.

Please help! Does anyone else have this trouble? This has happened from

Also the header always changes, adds return characters and moves the page number?!? - but that one is less likely to make me throw my computer against the wall.

[Charles Kenyon]

Formatting applied to one paragraph affects the entire document

[rooter]

I think that worked!!!!
You have no idea NO idea how grateful I am, thank you thank you, thank you!