9 Best PDF Encryption Software Tools, Compared by Encryption Strength

A user (open) password actually encrypts the file — with AES-256 and a strong password, the content is computationally infeasible to crack. A permissions (owner) password does not: it only asks the PDF reader to block printing or editing, and those restrictions can be stripped by readily available tools because the content itself was never encrypted. If your goal is genuine confidentiality, you need a user password, not just permission flags.

This is a selection guide, not a tutorial. Each PDF encrypter below is judged on the criteria that actually separate encryption tools, with a clear Best for / Skip if line.

Part 1. How We Judged These Encryption Tools

Five criteria decide whether a PDF encryption tool actually protects your file — and which encryption PDF option fits your document. Every tool below is rated against the same list:

• Encryption strength — AES-256 is the current standard (PDF 2.0 / ISO 32000-2); AES-128 is still safe for everyday use; 40-bit RC4 is broken. This is the single most important factor.
• Password types — does it support a true open (user) password for encryption, a permissions (owner) password for restrictions, or both?
• Platform — Windows, Mac, mobile, or browser; some tools are single-platform only.
• Beyond encryption — can it also edit, redact, and batch-process, or does it only set a password?
• Price & privacy — free, one-time, or subscription, and whether the file is processed locally or uploaded to a server.

Part 2. PDF Encryption Software Comparison at a Glance

The table states each tool's encryption ceiling and real limits, so you can match the tool to the sensitivity of your document.

Pricing, plans, and encryption options change with promotions and releases; confirm current figures and the exact AES level on each vendor's page before buying rather than relying on a fixed number here.

Part 3. Full PDF Editors with Strong Encryption (AES-256)

These secure PDF software suites encrypt to the current standard and also edit, redact, and manage documents — the right choice when encryption is one task among many and the file is sensitive.

1. UPDF — Best All-Round Encryptor + Editor

UPDF sets both password types from a single panel: an open (user) password that encrypts the file so it can't be viewed without the password, and a permissions password that restricts editing, copying, and printing. It supports standard PDF encryption from 128-bit RC4 up to 128-bit and 256-bit AES, so you can match the strength to the document. It also batch-encrypts PDFs — useful when you're locking a folder of contracts at once — and either password can be changed later. Beyond security, it's a full editor (edit, OCR, convert, annotate, organize) across Windows, Mac, iOS, and Android on one license.

It's not desktop-only: UPDF on iPhone, iPad, and Android can set a password too, so you can lock a file from the device in hand and the same license covers every platform.

The free tier adds a trial watermark when saving, so watermark-free encryption needs Pro. UPDF is priced well below the subscription-only suites, with both annual and one-time options — check the current price on UPDF's site, since promotions change it. The honest ceiling shared by every password tool here: encryption controls who can open a file, but can't track or revoke access once you've shared the password.

For the full walkthrough and other methods, see how to protect a PDF. Download UPDF for free to try it — installation is free, and Pro unlocks watermark-free export and batch encryption.

2. Adobe Acrobat Pro — The Enterprise Standard

Adobe Acrobat Pro encrypts to AES-256 and pairs it with the deepest document toolset here — redaction, comparison, signing, and certificate-based security for enterprise workflows. For organizations already on Adobe, it's the safe default.

The cost is the catch: Acrobat Pro is effectively subscription-only (around $239.88/year), and it's the heaviest app in this list. If you want comparable AES-256 without the price or the weight, see lighter Adobe Acrobat alternatives.

3. Foxit PDF Editor

Foxit PDF Editor supports both AES-128 and AES-256 with open and permissions passwords (and can save security settings as a reusable policy), wrapped in a ribbon interface that mirrors Microsoft Office. It runs on Windows, macOS, and the Web, and pairs encryption with OCR, redaction, and eSign/AI features depending on plan.

Limitations: it's a paid tool, and advanced security, mobile, eSign, and AI features vary by edition and plan — so confirm your plan includes AES-256 and the security features you rely on.

4. Nitro PDF Pro— Batch-Oriented Business Tool

Nitro PDF applies password security with a selectable encryption algorithm — AES-256 is available — using both open and permissions passwords, and its batch automation suits businesses locking large volumes of files. It runs on Windows, Mac, and iOS, with batch OCR, digital signatures, and AI tools depending on plan.

Licensing is the watch-out: the one-time Nitro PDF Classic is a three-year, Windows-only license.

5. PDF Expert — Polished Apple-Only Option

PDF Expert is a polished editor for the Apple ecosystem that protects files with a standard set-password flow and also annotates, edits, OCRs, converts, and signs. For Mac, iPhone, and iPad users who want a native-feeling app, it's a strong pick.

The hard limit: PDF Expert has no Windows or Android app, so it's a non-starter for mixed-device teams.

Part 4. Free & Single-Purpose Encryption Tools

These secure PDF tools cost nothing or do one job. They're fine for a quick lock, but watch the encryption ceiling — and remember that browser tools upload your file, which is the wrong choice for anything truly confidential.

6. Preview — Free and Built Into Every Mac

Preview is the default PDF app on every Mac, and it can encrypt during export at no cost — set an open or permissions password and save a protected copy. For a one-off lock on a Mac, it's the fastest free route. See how to password-protect a PDF in Preview.

The ceiling: Preview doesn't expose an AES-256 option — its encryption is AES-128 — and it's Mac-only with no batch processing. AES-128 is fine for everyday files, but for long-term sensitive data prefer one of the AES-256 tools above.

7. iLovePDF — Free Browser-Based Protection

iLovePDF protects PDFs from any browser with no install, and bundles other free tools (merge, compress, convert, split) alongside; it also offers desktop and mobile apps. It's handy when you just need a password fast on a machine where you can't install a full editor.

The trade-off is privacy: the online workflow uploads your file to iLovePDF's servers, and the free tier has processing limits. For contracts, IDs, or financial documents, use a local desktop tool instead — the file should never leave your device.

8. Cisdem PDFMaster — Mac Encrypt + Decrypt

Cisdem PDFMaster encrypts with open and permission passwords on Mac, and goes well beyond a simple lock: it edits, converts, OCRs, redacts, and can batch encrypt or decrypt files. For a Mac user who wants one app for security plus document work, it's a capable all-rounder.

It's less established than Adobe, Foxit, or UPDF, with a smaller user base and support ecosystem, and it's Mac-only — worth a look, but verify it fits your workflow before committing.

9. PDFEncrypt — Free, Open-Source, AES-256

PDFEncrypt is a free, open-source Windows utility that does one thing well: encrypt PDFs using standard PDF encryption, with AES-256 supported, at no cost and processed locally. It can even generate a strong random password for you.

It's single-purpose by design: no editing, no PDF redaction tool, no annotation, and Windows-only. If you need anything beyond encryption, pair it with a full editor or pick one of the suites in Part 3.

Part 5. Encryption Edge Cases to Know

Choosing a tool is only half the job. These situations trip people up regardless of which software they use:

• Permissions password isn't security. An owner/permissions password only asks the reader to block printing or editing — specialized tools can remove it because the content isn't encrypted. For real confidentiality, set an open (user) password.
• AES-128 vs AES-256. AES-128 is fine for routine files; choose AES-256 for anything sensitive or long-lived. Tools like Preview cap at 128; Acrobat, Foxit, and PDFEncrypt reach 256.
• There's no backdoor. If you set an open password with AES and lose it, the content is genuinely unrecoverable. Store strong passwords in a password manager before you encrypt.
• Encryption can't track or revoke. A password controls who can open a file, but once shared it can't stop forwarding, log who opened it, or revoke access. For that you need a document-rights or secure-sharing platform, not a password.
• Metadata may stay visible. By default, title and author metadata often aren't encrypted, so they can leak in file browsers. Use a tool's encrypt-metadata option if the filename or properties are themselves sensitive.
• Encryption isn't redaction. Locking a file with a password doesn't hide the sensitive text inside it — anyone with the password sees everything. To permanently black out names, numbers, or clauses before sharing, you need redaction software that removes the underlying content, not just encryption.

Part 6. FAQs

Conclusion

The right PDF encryption tool comes down to two questions: how sensitive is the document, and what else do you need to do with it? For anything confidential, insist on AES-256 and a real open password rather than permission flags alone. For a quick free lock, Preview (Mac) or PDFEncrypt (Windows) are enough; for encryption plus everyday editing across every device, UPDF covers both with open and permissions passwords, batch encryption, and a single license for Windows, Mac, iOS, and Android.

Download UPDF for free to try encrypting your own PDF — installation is free, and Pro features are available when you need watermark-free export or batch encryption.