Help! The file size of my document grew tremendously after embedding fonts!

Well I faced this problem just yesterday.

Embed only used characters
Firstly you probably have chosen to embed the entire fonts instead of only the characters in use. If you don't intend to edit the document, or the computer you will edit the document on already has the fonts, then you don't have to embed the entire font, which will reduce the file size significantly.

Replace unused fonts
But what if you really want to embed the fonts for editing? Then we have to see which fonts are being used, and replace them as necessary using the "replace fonts" tool in the office applications. PowerPoint/Word may think that some fonts are in use when actually they are not (or are used in some hidden places that do not matter) so you can replace them away and save the need to store yet another font. Note, however, that some fonts such as Wingdings may not appear to be used but are actually used for things like bullets, so you cannot replace them.

Stop embedding double-byte (Asian text) fonts
However most likely if the file grows beyond 10MB suddenly is due to the embedding of a double-byte (usually for Asian Text) font. This can happen if you accidentally type some Asian text into the document, and PowerPoint/Word switches to such fonts. Or perhaps you just made use of such fonts, even for Western characters. Each of these fonts can be 10-20+ MB, thus making the document size explode.

A solution is to replace the double-byte fonts with the smallest double-byte font you have (since you cannot replace a double-byte font with a regular font). For this purpose I have made (using a trial version of TypeTool) a font called Fake doublebyte font that contains only one Chinese character. Note that PowerPoint/Word recognizes the font as a Chinese font, so it only appears in the list if you try to replace a Chinese font and not, say, a Korean font. However we can make use of the font simply by typing the font's name into the box itself instead of selecting from the list in the "Replace Fonts" window.

Convert to HTML and replace font names
Some people have also suggested converting the document to HTML and then replacing the problematic font with another font in the HTML, but I've had some problems getting it to work. You might want to read the following links for more information about this: Why won't Replace Fonts work? Understanding Unicode fonts, How to find and delete embedded fonts in PowerPoint, Asian/Double-Byte fonts can't be replaced.