Encrypt a Document

What is this page about?

This page describes how to encrypt Word documents using passwords and various encryption algorithms.

Encryption is the process that translates readable text to meaningless sequences of bytes so it can only be read by the person who has the decryption key or the secret code. This process plays an important role in securing your content. It helps to encode the content, verify the origin of a document, prove that the content has not been modified after it was sent, and ensure that the data from the document is safe.

This article explains how Aspose.Words allows you to encrypt a document and how to check if a document has encryption or not.

Encrypt with Password

To encrypt a document, use the Password property to provide a password that functions as an encryption key. This will modify the content of your document and make it unreadable. The encrypted document will require to have this password entered before it can be opened.

You can find the appropriate Password property for the required format. Each document save format in the Saving Namespace has a corresponding class containing save options for this format. For example, the Password property in the DocSaveOptions class for DOC, or the Password property in the OoxmlSaveOptions class for DOCX, DOCM, DOTX, DOTM, and FlatOpc.

Note that only certain document formats support encryption. For example, RTF does not support encryption.

The table below lists the formats and encryption algorithms supported by Aspose.Words:

Format	Supported Encryption while Loading	Supported Encryption while Saving
DOC, DOT	XOR encryption40-bit RC4 EncryptionCryptoAPI RC4 Encryption	RC4 Encryption (40-bit)
DOCX, DOTX, DOCM, DOTM, FlatOPC, FlatOpcTemplate, FlatOpcMacroEnabled, FlatOpcTemplateMacroEnabled	ECMA-376 Standard EncryptionECMA-376 Agile Encryption	ECMA-376 Standard Encryption (AES128 + SHA1)
ODT, OTT	ODF Encryption (Blowfish/AES)	ODF Encryption (AES256 + SHA256)
PDF	-	RC4 Encryption (40/128 bit)

The following code example shows how to encrypt a document with a password:

Check If a Document Is Encrypted

In some cases, you may have an unreadable document and want to be sure that the document is encrypted and not corrupted or compressed.

To detect if a document is encrypted and if a password is required, you can use the IsEncrypted property of the FileFormatInfo class. This property will also allow you to perform some action before loading a document, for example, informing a user to provide a password.

The following code example shows how to detect the document encryption:

Open a Document With or Without a Password

When we have made sure that a document is encrypted, we can try to open this document without a password, which should lead to an exception.

The following code example shows how to try opening an encrypted document without a password:

After we have seen that an encrypted document cannot be opened without a password, we can try to open it by entering the password.

The following code example shows how to try opening an encrypted document with a password:

---

FAQ

1. Q: How do I encrypt a Word document with a password in C#?
   A: Create the appropriate save options object for the target format (e.g., DocSaveOptions for DOC or OoxmlSaveOptions for DOCX) and set its Password property. Then call Document.Save with those options. The document will be saved encrypted and will require the password to open.

2. Q: Which file formats support encryption when saving with Aspose.Words?
   A: Encryption is supported for DOC/DOT (RC4 40‑bit), DOCX/DOTX/DOCM/DOTM/FlatOPC families (ECMA‑376 AES‑128 + SHA‑1), ODT/OTT (AES‑256 + SHA‑256), and PDF (RC4 40/128‑bit). Formats such as RTF do not support encryption.

3. Q: How can I determine whether a document is encrypted before loading it?
   A: Use FileFormatInfo.IsEncrypted. Pass a stream or file path to FileFormatInfo and check the IsEncrypted boolean. This lets you prompt the user for a password only when necessary.

4. Q: What happens if I try to open an encrypted document without providing a password?
   A: Aspose.Words throws an IncorrectPasswordException. Catch this exception, inform the user that a password is required, and optionally request the password to retry loading the document.

5. Q: Can I change the encryption algorithm of an already encrypted document?
   A: Yes. Load the document using the existing password, then save it again with new save options that specify a different Password and, if needed, a different encryption algorithm supported by the target format. This re‑encrypts the document using the new settings.