If you have Acrobat (not the free acrobat reader), you should be able to insert comments (like sticky notes) into the document. But what it sounds like you are looking for is something to convert the .pdf into an editable document
If you type "pdf editor" into Google, you'll get about 17 million hits, of which there are a number of free and low cost pdf editor packages.
This one says it will convert a
pdf file into a word document for $29. Probably worth a try.