Blocking out unneeded information in a PDF?

As far as I know there is not such thing. However I can think of a way for you to do it, please keep in mind this not the intended use of the button tool but will help resolve your issue.
Can you make buttons in the version of acrobat you have? (tools menu> forms> button tool) If so, draw a button on top of the text you want to remove from the pdf, then in the new window that appears, in the "appearance" tab choose white for the fill color. Close the window. Click on the hand tool to see the result. A little hand will show every time you rollover the white square but nothing will happen since you did not apply any actions to the button, you are just using it to cover the unwanted text.If you can not make buttons in your acrobat version, consider using another image application software like photoshop or photoshop elements to erase the unwanted text.

Hope that resolves your issue.

For versions prior to version 8 there are 3rd party tools to redact information from PDF. Version 8 Professional introduced Redaction within Acrobat and version 9 Professional has extended this feature to include access through JavaScript, see url=http://www.acrobatusers.com/tutorials/2008/07/auto_redaction_with_javascript/]Automating redaction with Acrobat JavaScript[/url] by Thom Parker

[b][color=#FF0000]Do not[/color][/b] use the highlight tool or form tool or any other tool to cover any text or image in a PDF. The text will still be searchable underneath it in Reader/Acrobat and any user with a standard version can delete highlighting , and any user with the professional product can delete form fields. There are any number of instance in the past where newspapers and government agencies have caused the release of [b][color=#FF0000]very sensitive information[/color][/b] using this type covering.

Even MicroSoft has started to provide redaction for MicroSoft Office Products because it is so badly needed.

try this: use the drawing tool in the advanced comenting toolbar and mask the text to be redacted with a 100% opaque rectangle any color, even white. When you print, click the advanced button and select 'print as image' and click OK.