the redaction tool in Adobe Acrobat Reader:

• The process of permanently eliminating visible text and graphics from a document is known as redaction. To remove content, you use the Redact tools.
• You can use redaction markings in the form of coloured boxes to replace the removed objects, or you can leave the area blank. Over the redaction markings, you can specify custom text or redaction codes. To delete or redact sensitive images and text that are viewable in a PDF, use the Redact tools.
• To detect and delete hidden content from a PDF, use the Remove Hidden Information function.

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