You can only edit PDF files if you have the full application of Adobe Acrobat - most of us only have the reader version which enables us to look at the PDF files - but not edit them.
PDF files can be opened & edited in Photoshop if you know someone with this application.
There is a new programme called Solid Creator PDF I installed it from a CD on computer magazine but can't remember which one. This converts PDF files directly into Word where you can edit them.
PC World have a similar software on sale but it costs £50 approx.
The proper Acrobat programme costs HUNDREDS!!