Delete page grayed out along with other features in Acrobat XI PDF.

I designed a PDF form in Acrobat XI that keeps track of my professional development over a 5 year period. Each year my supervisor signs it with a digital signature. After he signed it the first time I noticed I was a lot of features were grayed out such as delete page, extract page, insert page and rotate page. I need to add pages to this document so I can attach evidence of my professional development each year. So when I complete a course or workshop I insert the certificate of completion at the end of the PDF. I also want to delete a few older pages. How can I regain these features but still work with signatures?