SumatraPDF review: a private way to read PDFs on Windows

SumatraPDF is a free open-source PDF reader for Windows that also opens ebooks and comics.¹ It suits people who want a straightforward way to read downloaded documents. For privacy-minded readers, its appeal is keeping everyday reading on their own computer, with some important exceptions explained below.

Last checked October 28, 2026.

At a glance

• What it is: A desktop document reader.
• Works on: Windows 7–11, with 32-bit, 64-bit and ARM64 downloads; ARM64 requires Windows 10 or 11.²
• Price: Free, with no ads or subscription.¹
• Licence: GPL v3 for most application code, with BSD exceptions and AGPL v3 requirements through MuPDF.³
• Best for: Reading PDFs, manuals and ebooks on a Windows computer.
• Official site: sumatrapdfreader.org

What SumatraPDF does and how it protects your privacy

Think of SumatraPDF as a reading tool for the files you already have. Choose it for a train timetable, an appliance manual or a long report when you want to concentrate on the pages. Supported formats include PDF, EPUB, MOBI, CBZ, CBR, DjVu, XPS and CHM.¹ EPUB and MOBI are ebook formats; CBZ and CBR package comic-book pages into one file.

The developer’s policy says normal document use does not upload documents, filenames or reading history.⁵ That is useful when you want to read a private letter without choosing an online document service. Keep the distinction between opening a file and deliberately sending its contents to another service.

Version history dates release 3.6.1 to April 6, 2026, lists 3.7 as next, and says those changes are available in pre-release builds.⁴ A pre-release is an unfinished version offered before the next regular release. Start with the 3.6.1 download unless you have a specific reason to try development features.

Key features of SumatraPDF

• Portable edition: Run the reader from a USB drive without installing it.²
• Custom controls: Adjust keyboard shortcuts and themes to suit your reading habits.¹
• Quick commands: Press Ctrl + K to find commands in the command palette.⁴
• Text highlighting: Select text and press a to highlight an important passage.⁷
• Saved annotations: Save notes and highlights into the PDF with Ctrl + Shift + S.⁷
• Remembered reading position: Per-file settings save your zoom, scroll position and view mode by default.⁶

SumatraPDF pros and cons

Pros

• A sensible starting point if reading is your main document task.
• One application handles both PDFs and several ebook formats.¹
• An installer and a portable download give you two ways to get started.²
• The code credits identify contributors including Krzysztof J. Kowalczyk and Simon Bünzli.³

Cons

• Windows only: there is no native Mac or Linux edition.¹
• When the program crashes, official builds send a crash report to the project’s website.⁵
• Reading can leave local traces, including cached page thumbnails.⁶
• Expect some learning time if you want to customize keyboard commands.
• A published security advisory lists version 3.6.1 as affected by a hostname-check flaw, and it names no patched version.⁸

Is SumatraPDF safe and private?

The official site credits Krzysztof Kowalczyk as its developer.¹ Public source code helps people inspect an application, but it should not be treated as a security guarantee.

Update checks are enabled by default and send version and system details; the server records the request with your IP address.⁵ An IP address is the network address seen by a server. Set CheckForUpdates = false in Advanced settings to disable those checks.⁵ If you do, make a habit of checking the official download page yourself.

Crash reports can contain document fragments and are deleted after 31 days, according to the policy.⁵ The policy also says optional AI chat sends document text to your chosen provider, while selection search and translation send selected text to another service.⁵ Treat those actions as a separate privacy decision, particularly when trying pre-release features.

Settings are stored in SumatraPDF-settings.txt beside the portable application or under %LOCALAPPDATA%\SumatraPDF for an installed copy.⁶ Consider who else can use that Windows account before reading confidential files. Plan separately how to protect the original documents, backups and any USB drive. For sensitive files, consider encryption: protection that requires a key or password to read the contents. Choose that protection separately from your reader.

According to the project’s July 2026 advisory, some HTTPS requests fail to verify the server’s hostname; an attacker would need a position on the network to exploit this.⁸ HTTPS normally checks that a connection reaches the intended server. Read this as a specific limitation, rather than assuming every network connection has identical protection.

How to get started with SumatraPDF

1. Open the official download page. Choose the regular release for your first installation.
2. Pick the recommended 64-bit download, or select ARM64 or 32-bit if that matches your computer.² Ask whoever manages your PC if you are unsure which kind it uses.
3. Choose the installer for your usual computer, or the portable ZIP for a portable setup. Keep the portable application in a dedicated folder so its related files stay together.
4. Launch the reader and open a familiar, non-sensitive PDF. Try a short manual before relying on it for an urgent document.
5. Adjust the reading size and try highlighting a passage. Save a highlight with Ctrl + Shift + S, then reopen the document to check the result.⁷ Practice on a spare copy first.
6. Review the privacy settings and decide whether automatic update checks suit you. Before using any online helper with private material, consider whether you want to share the selected text.

Who should use SumatraPDF, and who might prefer something else?

Choose SumatraPDF when you mainly want to read on Windows and prefer a portable option or a reader you can customize. Try it with a typical week’s documents before changing your default application. Include one long report and one ebook, rather than judging it only from a single-page receipt.

For a different workflow, compare Sioyek when research papers dominate your reading. Consider PDF Arranger for page-arrangement tasks, or calibre when choosing an ebook-library tool. Start with the task you need to finish, then compare the relevant guide.

Frequently asked questions

Is SumatraPDF free?

Yes: the official site describes it as completely free and open source.¹ There is no need to buy a subscription to start reading.

Does SumatraPDF work on iPhone or Android?

No: SumatraPDF is a Windows-only application.¹ Choose it for your Windows computer and look separately for a phone reader.

Does portable SumatraPDF leave reading history?

Portable mode stores the settings file in the same folder as the program, and page thumbnails in a sumatrapdfcache subfolder.⁶ Keep that folder private when sharing a removable drive; portable should not be read as trace-free.

Can SumatraPDF highlight PDFs?

Yes: text highlighting is available through the a shortcut after selecting text.⁷ Try it on a copy of your document, save the change and reopen the copy before using it for important notes.

Sources

1. SumatraPDF: Free, Fast PDF Reader for Windows
2. SumatraPDF: Download Free SumatraPDF 3.6.1
3. SumatraPDF repository: AUTHORS and licensing
4. SumatraPDF: Version history
5. SumatraPDF: Privacy policy
6. SumatraPDF: How we store settings
7. SumatraPDF: Editing annotations
8. SumatraPDF on GitHub: TLS hostname validation advisory