Скачать или смотреть How to Lock a PDF After Filling Out Text Fields in iText7

Discover how you can securely lock a PDF document after filling out form fields using iText7 in Java. Understand the limitations and alternative methods to ensure data integrity.
---
This video is based on the question https://stackoverflow.com/q/78224003/ asked by the user 'tanja' ( https://stackoverflow.com/u/23333130/ ) and on the answer https://stackoverflow.com/a/78224237/ provided by the user 'mkl' ( https://stackoverflow.com/u/1729265/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, comments, revision history etc. For example, the original title of the Question was: Locking PDF after filling out text field

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Locking a PDF After Filling Out Text Fields: A Guide Using iText7

In today's digital world, PDFs have become a common medium for sharing documents. Often, these documents have interactive elements such as text fields that recipients can fill out. However, once a recipient has entered their information, you might want to ensure the integrity of that information by locking the PDF. This guide addresses a common query: Is it possible to lock a PDF file after filling out a text field using iText7 in Java? Let’s dive into the details.

Understanding PDF Locking

When we talk about "locking a PDF," we are referring to the Modification Detection and Prevention (MDP) mechanism. This essentially restricts any changes to the PDF once it has been locked. There are two main ways to lock a PDF:

Locking the whole PDF: This lowers the MDP value of a PDF to 1, which means no changes are allowed except for updates of the Digital Signature Store (DSS) and document time stamps.

Locking individual fields: This is a more granular approach where specific fields within the PDF are locked to prevent alterations.

Both methods require applying signatures with DocMDP or FieldMDP transforms to the PDF. This means that without a signature on the document, MDP cannot be applied.

The Challenge of Locking Text Fields

Given this background, it’s essential to clarify that locking plain text fields in a PDF is not achievable in the same way as locking signature fields. When trying to implement locking after a text field has been filled in:

The straightforward answer is no, it is not possible to apply a locking mechanism like MDP directly on plain text fields.

Alternative Solutions for Locking Fields

Although you cannot achieve locking for text fields using MDP, there are several alternative strategies that you can employ to protect the integrity of your PDF data:

1. Set Fields to Read-Only

You can use iText to set all fields to read-only once a specific field has been filled. This means that while users will still be able to view the information, they will not be able to make any edits afterwards.

2. Flatten the Form

Flattening the form will convert all the form fields into regular content on the page. After flattening, users can no longer interact with these fields, effectively locking the information in place.

3. Add JavaScript Restrictions

You have the option to incorporate JavaScript within the PDF that can help prevent specific operations. For example, you could prompt warnings or alerts that restrict users from making certain changes.

Limitations of Workarounds

While these alternatives help in maintaining data integrity, it's important to know that they can be easily overridden. Additionally, any modifications made to bypass these restrictions might also invalidate the associated signature, thereby compromising the document’s authenticity.

Conclusion

In conclusion, while direct locking of plain text fields in a PDF using iText7 is not feasible via traditional MDP methods, there are alternative approaches available that can help you manage and secure the data effectively. By setting fields to read-only, flattening forms, or implementing JavaScript restrictions, you can retain a level of control over the information in your PDFs.

By understanding the limitations and leveraging these workaround methods, you can ensure the integrity of the data included in your PDF documents. So, whether you're designing forms or distributing important documents, you can now make informed decisions about how to manage and protect the data within your PDFs.