In previous versions of Word, I could just put my cursor into a paragraph or select the whole paragraph, and change the tab settings - it wouldn't change the settings of any other paragraph. In Word 2007, changing the tabs setting updates the whole document. How can I restrict my changes to a single paragraph?
Word 2007 didn't introduce any new behavior regarding this. When you select or place the cursor inside a paragraph, any paragraph-wide formatting will be applied to that paragraph only, retaining the integrity of the rest of the document.
Now, what you are almost certainly experiencing is a problem with the automated update feature for styles. This is an old feature (as old as styles in Word) that, once enabled, means any formatting changes to a paragraph using that style, will update the style definitions, which results in the remaining paragraphs using this style to be updated.
Let's get over with the simplest of cases:
Hopefully this is enough for you. If not, read on...
Some users have this problem with the Normal style. Which is very odd. I'm actually unsure as to why that would happen. If you right-click the normal style and select modify, you will see you don't have that checkbox. This style cannot be set to update automatically. But with some people it does(!).
To fix this issue:
The new document will behave as you want it to.
It's possible that when you open a new Word document when firing word.exe, the problem will resurface either on the same regular style, or the Normal style (whichever was your case). To fix this, you'll need to update your Empty Document Template. To that effect:
New documents will now behave.