Why does this document open in the wrong program?

If you double-click on a document and it opens in a program you don't want to use (for example, you have a .doc file that launches Word, but you want to work on it in Pages), you can drag and drop the document onto the Dock icon of the program you want to use, and let go when the program icon darkens. Then the document will open in THAT program, if the document is compatible. (If the program icon does not darken, then the document is probably not compatible with that program.)