Can't delete or insert pages, help?

I have made some corrections to a Word document that I previously made into a pdf document.

I saved the Word document to a new pdf with a new file name.

However, this time Adobe will not allow me to delete pages nor to insert pages nor to alter the text in any manner.

Those options are all greyed out.

I do not have the original word document on any kind of required permissions.

For some reason, the pdf has missing text at the top of 3 pages in succession. I'm trying to delete those 3 pages and replace them with a page one at a time.  I had to do this once before to the earlier version, but that time I was allowed to add and delete.

Please tell me how to fix this annoying problem.

Many thanks.