Apple - Blacking out a part of a PDF, or redaction of text

If you are looking for a no-cost way in Preview.app

1. File->Export (or save as)
2. Export PDF to TIFF file format (it's a multipage image format)
3. Open TIFF file
4. Export TIFF to PDF file format

Maintains page structure, OCR will be lost.

If you want to leave it as a PDF, you really need to use the actual redaction tools in Adobe Acrobat, otherwise you are simply leaving yourself open to reversals.

http://blogs.adobe.com/security/2009/12/how_to_properly_redact_pdf_fil.html

If you want to save the PDF as a graphics file, then any black box over the words should work.

A free solution, is to convert the PDF to an image, then save it as a PDF again. The only drawback is that the PDF will remove any OCR info it might have had.

Steps:

1. Open the PDF file to redact in Preview.
2. Black out text using any method you want (e.g. use the rectangle annotation tool with black as the color and choose the thickest border. Then draw the shape as many times as needed until your document is blacked out.)
3. File > Save As, and choose an image format such as PNG or GIF.
4. Open the saved image file, then File > Save As, and choose PDF.