To encrypt a PDF and keep your documents secure, you can use an online tool like pdf.net, Preview (Mac), or Microsoft Word.

This is a helpful way to protect your documents from unauthorized use, editing, and sharing. Additionally, encrypting a PDF will keep your sensitive data safe, which can also help you align with data protection policies set in force by the government or other institutions.

If you're new to PDF encryption, this guide covers why it matters, how encryption levels like AES-128 work, and how to encrypt a PDF both online and offline.

Key Takeaways

PDF document encryption is a safety procedure that helps you secure confidential information and restrict PDF access, usage, editing, and sharing.
Encrypting PDFs can help you protect documents and comply with the most widespread security regulations (HIPAA, GDPR, CCPA, etc.).
pdf.net secures your files with AES-128 encryption, the same standard trusted by banks and healthcare providers.
In addition to encryption, our software allows you to add signatures to your PDFs for extra security, but also modify, highlight, and annotate text based on your needs.

3 Reasons Encrypting a PDF Is Important

Encrypting a PDF is important because it protects sensitive information, limits the document's use, editing, or sharing, and helps you stay compliant with various security regulations.

Let’s learn more about the encryption benefits:

#1. Protecting Confidential Information

You can encrypt PDFs to keep specific information a secret; this process renders data into unreadable text, which users can only access if they have the correct password.

Encryption is especially important for highly confidential documents, as it can prevent data leaks. For instance, it is recommended when securing medical and business documents containing sensitive data such as patient diagnoses, employee salaries, and trade secrets.

Not protecting your files can lead to the revelation of such information, which can cause serious problems, damage a company’s or person’s reputation, or affect your future professional endeavors and collaborations.

Similarly, encryption protects you from identity theft, which is a common threat nowadays, as it allows you to secure personal information such as your ID card number and SSN.

And finally, PDF metadata also poses a risk of identity theft because it can reveal personal information (e.g., data about the PDF author). You can edit PDF metadata or use encryption to make them inaccessible, both of which are practical ways to make your personal details safe.

#2. Preventing Unauthorized Editing or Sharing

PDF encryption can also help you set various restrictions for your files and prevent unauthorized access. This can also prevent illegal sharing, because even if your file ends up where it should not be, no one can retrieve the data without the decryption password.

For example, if you sell books in the PDF format online, you can encrypt each copy and share the passcode for decrypting it with buyers.

Not having access to encrypted files also makes such PDFs non-editable and prevents any modifications to your files. Some PDFs contain instructions that must stay unchanged. Encryption ensures your files remain intact and functional.

Moreover, using encryption to protect intellectual property is a top priority for businesses and professionals. Otherwise, business competitors, hackers, and other individuals with malicious intent can copy and use patents, designs, and scientific discoveries without authorization.

This can hurt the creator’s business and revenue. In some cases, misuse of intellectual property may even endanger others.

#3. Compliance with Data Security Regulations

Encrypting your files is the easiest way to comply with strict data security policies that certain countries and companies propose.

Let’s check out some well-known security regulations:

CCPA. The California Consumer Privacy Act dates from 2020 and regulates consumer rights, allowing them to know what data is gathered or sold and for what purpose.
GDPR. The General Data Protection Regulation, enacted by the European Union in 2018, requires organizations to protect the personal data of EU citizens and residents and gives individuals the right to control how their information is collected, stored, and shared.
HIPAA. The U.S. Department of Health and Human Services issued this act in 1996 to protect sensitive information in the medical industry. It grants individuals the right to know and decide how their medical data is used.
PCI-DSS. The Payment Card Industry Data Security Standards are a non-governmental regulation created by the leading credit card companies. It ensures privacy protection with quarterly vulnerability scans and annual assessments, which help perform transaction audits.

So, if you fail to encrypt your documents, it might lead to unauthorized data exposure and the breach of regulations, where individuals responsible may be charged with criminal offenses.

How to Encrypt a PDF Online

To encrypt a PDF online, you can use pdf.net, and here’s how to do it step by step:

Go to our Protect PDF tool and click on the Choose file button to upload your PDF manually or drag and drop it into the box.
Once you upload your document, you’ll be prompted to set a password.
Type in your passcode and click the Set password button.
To save your PDF, click the Download button in the top-right corner. The process is automatic and takes a few moments to complete. After this, you will find your encrypted file in your default download folder.

Our tool secures every file with AES-128 encryption, giving your documents bank-level protection the moment you set a password.

How to Encrypt a PDF on Mac with Preview

To encrypt a PDF on Mac with Preview, follow these steps:

Open your PDF in Preview.
Click File, then Export.
Select Permissions and check Require password to open document box.
After that, type in and verify your password, and click Apply.

However, keep in mind that this method only works on macOS and doesn't include the unlocking, signing, or editing tools that come with pdf.net.

How to Encrypt a PDF Using Microsoft Word

Encrypting a PDF using Microsoft Word works well for simple files, but converting a PDF to Word and back can shift formatting in documents with complex layouts, tables, or images.

That said, here’s how to do it step by step:

Open the PDF in Word (Word converts it into an editable document).
Click File > Print, go to the PDF drop-down menu, and select Save as PDF.
Click PDF Security Options, check Require password to open document box, enter your password, and click OK.

PDF Encryption Levels: AES-128 vs. AES-256

The strength of your PDF protection depends on the encryption standard behind it, and understanding the difference helps you choose a tool you can actually trust.

AES (Advanced Encryption Standard) is the current benchmark for PDF security, replacing older, weaker methods like RC4 algorithm, which is now considered breakable with modern computing power. There are three AES encryption types (128, 192, and 256), but the two relevant for PDF encryption are:

AES-128 which encrypts your file using a 128-bit key. It's the encryption level pdf.net uses to protect every file you secure, and it's the same standard trusted by banks, healthcare providers, and government agencies.
AES-256 uses a longer, 256-bit key, making it mathematically even harder to break. It's often reserved for highly classified files, though the practical difference in everyday document security is minimal since brute-forcing either standard is already unrealistic.

For most personal, business, and compliance needs, AES-128 encryption offers more than enough security to keep your documents safe.

Owner Password vs. User Password: What's the Difference?

PDF encryption actually relies on two different types of passwords, and knowing the difference explains exactly what your encrypted file will and won't protect.

User password (also called an open password) controls whether someone can open the file at all. Without it, the PDF stays completely unreadable, this is the type of password our tool creates for you.
Owner password (also called a permissions password) doesn't block access to the file. Instead, it restricts what a reader can do once it's open, such as printing, copying text, or editing the document.

It's worth knowing that permissions set with an owner password can sometimes be bypassed with third-party software, since the file itself isn't locked. If keeping unauthorized readers out entirely is your priority, a user password is the stronger choice.

5 Tips for Creating a Strong Encryption Password

Even AES-128 encryption is only as strong as the password protecting it. Follow these best practices when setting yours:

Use at least 10-12 characters. Longer passwords are exponentially harder to crack through brute force.
Mix character types. Combine uppercase and lowercase letters, numbers, and symbols.
Avoid personal information. Skip names, birthdays, or anything easily guessed or found on social media.
Use a different password for each sensitive document. Reusing the same password means one leak compromises every file it protects.
Store it in a password manager. This keeps your password strong and memorable without writing it down somewhere unsecured.

What Else You Can Do with pdf.net

Besides encrypting your documents, our online PDF editor allows you to modify them further in terms of security, readability, and many other aspects.

Here are the main features for tweaking PDFs to perfection:

#1. Unlock and Decrypt

If you know the password for an encrypted PDF, our Unlock PDF tool lets you remove that protection in seconds. Simply upload your file, enter the current password, and download a fully accessible, editable copy.

However, keep in mind that pdf.net cannot unlock a PDF if you don't have the password. This applies to any properly encrypted file, including one you protected yourself using AES-128 encryption.

In addition to removing the password itself, you can also remove PDF restrictions once you have access to the file. For instance, if a PDF was made read-only, you can make its text copyable again, permit editing, or turn printing back on.

#2. Sign

pdf.net offers another way of protecting your files by adding signatures, which enhances the document's credibility. First, you can sign your PDFs by placing unremovable signatures on them.

Additionally, you can add PDF watermarks and logos for authenticity, branding, and safety purposes. The software allows you to adjust the opacity and position of watermarks and logos, as well as use the batch-processing feature.

#3. Edit Text

If you want to add, remove, or replace text in your PDF, our text editor is the right tool for you. It also allows you to change font size, color, and style according to your preferences. Moreover, proofing and similar processes are much easier with our annotation software for adding comments and sticky notes, with the ability to customize their position.

You can also expand your proofing process by highlighting your PDF document. Our tool offers various colors and pen shapes, enabling you to highlight text with precision and easily draw different shapes.

#4. AI Tools

Chat PDF is one of the most innovative options because it allows you to analyze and summarize your PDFs, as well as ask questions about your file to request further explanations. Plus, you can ask for different types of analyses (e.g., content distributed in tables or bullet lists).

Even more, our AI can generate PDFs from scratch or translate texts from English into numerous languages, including Italian, German, Spanish, and Portuguese, and vice versa.

Final Thoughts

PDF encryption provides the highest security levels to your documents, which helps you protect your data and prevent unauthorized file use or sharing. Whether you choose an online tool like pdf.net or a built-in option like Microsoft Word or Mac Preview, encrypting your PDF only takes a few minutes and goes a long way toward protecting your data.

As a result, you can avoid data leaks, identity theft, and other repercussions such as a damaged reputation caused by information leakage.

How to Encrypt a PDF FAQs

#1. Can I remove encryption from a PDF later?

Yes, you can remove encryption from a PDF only if you know the original password. Aside from this scenario, it is impossible to reverse this process.

#2. What happens if I forget my password?

If you forget your password, you will not be able to access your PDF. Our unlock tool can only remove a password you already know; it cannot recover or bypass a forgotten one, regardless of the encryption level used.

#3. Is PDF encryption safe from hackers?

Yes, PDF encryption is safe from hackers when it's backed by a strong standard like the AES encryption, which would take far longer than a hacker's lifetime to crack through brute force. On the other hand, your PDF encryption may be easy to breach if you use cheap tools for the same purpose.

#4. Can I encrypt a PDF on my mobile device?

Yes, you can encrypt a PDF on your mobile with pdf.net since it’s fully browser based. No need for software installation or steep learning curves.

#5. What's the difference between password protection and encryption?

Password protection and encryption are closely related but not identical: password protection is the access control (the password itself), while encryption is the underlying technology that scrambles your data so it can't be read without that password. When you password protect a PDF with pdf.net, both happen together.

#6. Does encrypting a PDF increase file size?

Encrypting a PDF increases its file size only slightly, typically by less than 1%. The added data comes from the encryption key and security metadata, not from any change to your document's content or quality.

How to Encrypt a PDF and Keep Your Documents Secure