WordDump is an application for extracting all the words from documents, or text selections, and presenting them as a list, optionally accompanied by their frequency in the document.
Better yet, the WordDump app also provides this function conveniently as a Service, in any app Services menu or its contextual menus, along with other other auxiliary service functions explained below. As a service you can apply the functionality to text selections in an app that support services, such as Safari or TextEdit.
The extracted word list can be ordered alphabetically or by their frequency in the document. Supported document formats include Text, PDF, MS Word, HTML, RTF, and RTFD, but any document that can be indexed by Spotlight is supported by WordDump.
Once the application is installed, and run once, the Keyboard System Preference pane can be used to access Services Preferences.