This plugin adds a text input on the Edit submission page, into which students must manually enter the word count for their submission. The input is required, and only accepts numbers (up to a generous/ambitious eight digits in length).
This wordcount is shown on the assignment page submission status, and grading pages.
Warning: Using this plugin breaks the assign submission requirements routine. E.g. with both this wordcount, and the file submission plugin enabled, a student could create a submission with a wordcount, but no file upladed. Please see https://tracker.moodle.org/browse/MDL-47880 for more details.