Privacy First
Uploaded files are automatically and permanently deleted within two hours.
Automatic deletion
Encrypt PDF
Add an open password to any PDF with AES-256 encryption – by default directly in your browser, so the document never leaves your device.
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Local: By default the PDF is encrypted in your browser and not uploaded at all.
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Strong: AES-256 encryption as defined in PDF 2.0, readable in every modern viewer.
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Simple: Choose a password, confirm it, download – no account, no watermark.
PDF password protection
Password-protect a PDF without uploading it
Choose a PDF, set a password in the dialog and download the protected copy. Encryption uses qpdf compiled to WebAssembly, so the whole process happens inside your browser by default; if your device cannot run it, the same qpdf engine encrypts the file on our server and deletes it afterwards.
How to use Converter App
1
Choose the PDF
Drop the file into the box or import it from Google Drive. With local encryption the file stays in your browser memory only.
2
Set and confirm the password
Use 12 or more characters or a few random words. The password becomes the open password of the PDF – without it the file cannot be displayed.
3
Download the protected PDF
Open the result once to check the prompt, then share the file and the password through separate channels.
Key features
AES-256 (PDF 2.0)
The strongest encryption the PDF standard offers. Supported by Acrobat Reader, Chrome, Edge, Firefox, macOS Preview and all current mobile viewers.
Nothing leaves your device
In the default local mode the PDF is read and encrypted with WebAssembly in your browser tab; no upload takes place, which you can verify in the browser's network tools.
Same engine on the server
Older devices or very large files can use the server mode: identical qpdf command, upload over HTTPS, automatic deletion after 30 minutes (upload) and 2 hours (result).
Content untouched
Pages, images, bookmarks, links and form fields are encrypted as they are – no re-rendering, no quality loss, no watermark.
Experience & privacy
Built for reliable document conversion.
Backed by 10+ years of engineering expertise in large-scale data and scientific computing, it’s built for real-world document workflows that require accurate layout preservation, strict privacy, and dependable, high-level performance.
Trusted by Users
Rated 5 stars on Trustpilot for speed, reliability, and ease of use.
User trust
Academic Use
Referenced in published research and used for interview transcription and qualitative data analysis.
Research use
How PDF encryption works
Since PDF 1.7 extension level 3 and PDF 2.0, documents can be encrypted with AES-256. The password is turned into a key with a salted hash (SHA-256 based), and every stream and string in the file – page content, images, fonts, metadata – is encrypted with that key. A viewer that opens the file must prompt for the password, derive the same key and decrypt on the fly. Converter App uses qpdf, an open-source PDF library, to apply this encryption: in the browser as a WebAssembly build, on the server as the native program.
Why the local mode is the default
Most 'online' PDF tools upload your document to a server first. For a tool whose only purpose is confidentiality that is a contradiction. In local mode the page loads the qpdf engine into your browser, reads the PDF from your disk, encrypts it in memory and hands you the result as a download – there is no network request with the file in it. The server mode exists as a fallback for devices that cannot run the engine, and it deletes uploads after 30 minutes and results after 2 hours.
Before you encrypt: a short checklist
- Finish all edits and signatures first; an encrypted PDF cannot be changed without the password.
- Remove content you do not want to share – redact it properly, do not just cover it with a box – and check the document properties for names and comments.
- Keep an unencrypted master copy in a safe place; the encryption is irreversible without the password.
- Test the result: open the downloaded PDF once and enter the password.
Password protection vs. encryption
'Password protection' is often used for two different things. Permission flags (no printing, no copying) are a request to the viewer and offer no real protection. Encryption with an open password mathematically prevents reading the content without the key. Converter App applies the second kind only, so a protected file is actually private – and that is also why a forgotten password cannot be recovered.
FAQ
Frequently Asked Questions
What exactly does the password protect?
The password you set is used as the PDF's open password (also called user password). The complete file content is encrypted with AES-256; a viewer must ask for the password before it can show a single page. The same value is also set as owner password, so the file is not left with weaker permission-only protection.
Local or server encryption – which should I use?
Keep the default local option whenever possible: the PDF never leaves your device, which is ideal for contracts, medical or HR documents. Local mode needs a browser with WebAssembly (all current browsers) and enough memory for the file. If it fails – typically on very old phones or with PDFs of several hundred megabytes – the tool offers the server option, which uses the same qpdf engine over an encrypted connection and deletes the upload automatically.
Can I set permissions such as 'no printing' instead of a password?
Not with this tool. Permission-only restrictions (owner password without open password) are enforced by the viewer, not by encryption, and are removed by any PDF unlocker in seconds. Converter App therefore only offers real encryption with an open password, which actually keeps the content private.
What if I forget the password?
There is no back door. AES-256 with a long password cannot be cracked in any practical time, and Converter App does not store the passwords it was given. Keep an unencrypted copy of important documents in a safe place and use a password manager for the password itself.
The PDF already has a password – can I change it?
A PDF that already asks for an open password is rejected with a notice. Remove the old password first with the Unlock PDF tool (you need the current password), then encrypt the unlocked copy with the new one. PDFs that only have owner restrictions are accepted and re-protected with your new password.
How secure is the password I choose?
The encryption is only as strong as the password. Use at least 12 characters or three to four unrelated words; avoid reusing a password from another service. Send the password through a different channel than the file – for example the PDF by email and the password by phone or messenger.