Here's a neat trick to add Pinyin or Zhuyin to any Chinese text. In Microsoft Word, paste some Chinese characters.
Select all the text (CTL A) and click on the file menu: Format > Asian Layout > Phonetic Guide.
The selected text will have phonetics, and there are a few options for positioning them and changing their size.
If you are seeing Zhuyin phonetics and would prefer Pinyin, (or vice versa) you may need to change the formatting of the Chinese characters. Select the text, click on the file menu: Format > Reveal Formatting. In the sidebox that pops up, you can change the language settings to PRC for Pinyin or Taiwan for Zhuyin.
If you still can't see the Pinyin phonetics, you may need to install MSPY (Microsoft Pinyin Input Method), available from the Microsoft website: http://www.microsoft.com/china/windows/products/ime/MSPY2007.mspx
You can find more information about this feature from Pinyin Joe's Chinese Computing Help Desk.

Comments
Nice tip. For Word 2007 users, it’s not easy to find command for Phonetic guides. Just add a button. From the Office button, choose Word Options, Customize. Choose “All Commands” and select Phonetic Guide and click OK.
Thank you Jim. As you put it, ‘nice tip’ and this applies to Qiu Gui’s original and to your addition.
I use Vista Word 2007 and, using your comment, achieved the desired result – but only partly.
If I key in one word (or more) using pinyin and the usual candidate selection, it works fine – and what a pleasure it is!. But if I just copy and paste a selection of previously written characters these appear on the one line in the ‘Phonetic Guide’, I do not get the pinyin, and the fields in the ‘ruby’ column stay stubbornly blank.
Am I expecting too much or is there a way this (copy and paste)can be made to work?
I would much appreciate your, or Qiu Gui’s comment.
Leo
Do you know how to put the phonetic guide below the characters? Please email to me ok?