Sometimes, working with PDFs can be frustrating, because of the limitations on the files themselves. There is a website (and probably many others like it) that will help you making changes to PDFs:
or, try:
Now, a couple of things to note when you use these sites (or other sites like them):
1) Be careful what type of data you're uploading. It's easy to get careless since it doesn't seem like anything is actually leaving your PC - but you are transmitting information to these websites and I wouldn't send anything --if I were you-- that I wouldn't want the world to see.
2) If you are wanting to work with a PDF and you know who created it --especially if it has sensitive information in it-- then you might be better off to ask the creator of the PDF to make the changes that you'd like to see.
3) Many times, the changes that you would like to see are changes that you can accomplish yourself by other means. For example, if you want to add some handwritten notes to a PDF, just print it, write on it, and then scan it with one of the copy machines in the district. Or, if you want a PDF to be smaller, just open the file and then print the file --selected pages-- to a new PDF file.
Hopefully, some of this advice will help you as you continue to learn to deal with PDFs.