I was able to "Mark for Redaction" but the "Apply Redactions" button is no available. It is still gray.
What do I need to do in order to make these redactions permanent?
Sorry for the delay in response.
Open the document in Acrobat>File>Properties>Security tab, check under Document Restrictions Summary if you have permission to make the changes to the document. It clearly seems the document might be secured. Let us know if that helps.
If you already have found a solution to this problem, please update the thread with your findings that will help others.