How to Redact Text in a PDF

Introduction

Redaction means obscuring or hiding text to conceal sensitive information that would otherwise be divulged.

Sensitive information may cover a broad spectrum of categories, which include:

• PII - Personally Identifiable Information
• PHI - Protected Health Information
• Trade secrets
• Intellectual properties
• Financial information

When developing a data privacy strategy, the data redaction is considered a key factor. However, there are two important challenges revolving around the redaction process:

• Identifying the sensitive information.
• Applying the appropriate redaction technique.

Redaction techniques

When dealing with a PDF document, the data redaction consists of selecting a block of text and replacing the latter with a black rectangle. This will completely remove this block of text from the PDF document, in the same manner as blacking out a block of text with a permanent marker in a hard copy paper.

In some cases, we may come across redaction issues when we try to obfuscate confidential information in a PDF document by obscuring or covering such information. While such an approach works for hard-copy documents, it is not suitable for a PDF document, since there are techniques to extract the hidden information from the processed PDF document.

Scope

This lesson is intended to demonstrate the steps required for developing a PDF redactor. This will allow you to search for a specific word or phrase of interest in a PDF document and to hide it by replacing it with a black rectangle.

Please note that once we apply redaction to a PDF document, we cannot reverse this operation, in contrast with the PDF annotation function.

Process flowchart

The following figure exhibits the flowchart of the process to be developed: