Redact by Removal in Preview?

Since Preview is not a PDF Editor, you cannot properly redact text, as you can in Acrobat Pro, or PDFpen/PDFpen Pro (Mac App Store). All efforts to plaster over the text in Preview, with colored shapes, etc. still leave the searchable text in the PDF, and doom correct redaction.

For educational purposes, here is Adobe's article: Removing sensitive content from PDDs in Adobe Acrobat DC.

No. Preview is not an editor.

Easy enough to copy and paste a blank in Preview...

A true PDF editor, like "PDFpen.app" is well worth the $$ if this is part of your work flow:

https://smilesoftware.com/pdfpen

Sorry, I thought you meant remove the text. It's easy to cover it using a color other than black. You just use the eye dropper tool to click on the color you want to match.