Removing non standard characters from form input

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I have a form in which a user is entering input. Sometimes it will contain weird ASCII characters. Most likely the user is copying text from a Word document. For example:

 

This is some text  

 

How would I remove those extra characters from the string before taking the data and sticking in a database (as an example)? Basically, after submitting the form I want to remove those characters and then continue processing the string.