For those of you who come across PDF documents in which the document's creator has restricted the ability to copy text to the clipboard, here's a simple workaround: Highlight the text, then from the application menu (i.e. Preview or Acrobat) choose Services -> TextEdit -> New Window Containing Selection. Now you can copy and paste from the new "Untitled" TextEdit window. Sometimes it is just that simple.
[robg adds: We covered another technique in an older hint. There are legitimate reasons for doing this, such as wanting to reformat the text, being able to print the document's contents (if that feature was also disabled), or maybe to combine pieces of several documents into one personal-use-only combined document. As long as you're using what you create yourself, and not sharing it with others, there shouldn't be any copyright concerns.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040622214927503