Limitations
PDF only. The encryption key length is 128 bits.
TX Text Control .NET for WPF Reference GuideTXTextControl Namespace LoadSaveSettingsBase Class UserPassword Property
Specifies the password for the user when the document is reopened. If the password is an empty string the document can be reopened by every user.
Introduced: 11.0.
public string UserPassword { get; set; }Public Property UserPassword() As StringPDF only. The encryption key length is 128 bits.