Redaction is available only in the Advanced edition of Power PDF.
Use the Mark Redaction tool in the Security ribbon to first mark content for redaction, so the planned deletions can be reviewed.
Use the Apply Redaction tool when reviewing is completed, to permanently and unrecoverably render the data unreadable by applying redaction.
Areas to be redacted are marked by red rectangles, whereas already redacted areas are indicated by colored blocks; by default these are black.
Visible contents including text, graphics and images can be redacted. The appearance of redacted items can be modified. They commonly appear as colored boxes filled in with solid color, but you can also set them to display overlaid privacy codes, custom text, or just a blank area.
To mark and then permanently redact content from your document
Click Redaction Properties at Security > Redaction for the Redaction Tool Properties dialog box.
Use it to set your redaction mark appearance. See Setting Redaction Properties.
Select the Mark Redaction tool shown above.
To mark the text content you want to remove, move your pointer over it. When the cursor changes to 
, select the text to be removed.
To remove an area with no text (maybe a picture), move the cursor to it. When it changes to 
, draw a rectangle to cover the desired selection area.
Hold the pointer over a marked area to preview how the redaction marking will look when applied.
After review, right-click in a marked area and select Apply from the shortcut menu to apply redaction permanently to that area. If you want to make all marked redactions in the current PDF permanent, select Apply All.
Confirm redaction by clicking Apply in the dialog box that warns redaction cannot be undone.
Notes
Redaction cannot be undone once applied. To avoid mistakes, we strongly advise you to make a copy of the original PDF before you perform redaction; or save the redacted PDF as a new file with a different name and/or location.
Conversely, if you mark and/or apply redaction to a document, but then close it without saving, all the redaction work is lost.
Redaction can be done by searching and combined with document flattening or removing document elements. See About Redaction.