What software do I need to modify PDF files?

Depending the size of your document, one page, many pages? If this is not many pages, you can build again your document.

First OCR your Acrobat document, if possible, so you can copy and paste the text in your Illustrator or Indesign. Of course you have to know a little to use those softwares, but the basic use is not too complicated. You can also insert the pictures etc and then you can save as PDF in Illustrator or in Adobe PDF Preset in Indesign save your new PDF.

If you have Adobe Master Suite, you may have Indesign, or you may use Illustrator.

You may google some tutorials to do some basic works with these two softwares.