The Tools package comes with a basic DigitalSignature tool that allows signing with a specific keystore and password. The DigitalSignature tool can be used with the UI components such as DocumentActivity and PdfViewCtrlTabHostFragment2. You can also use the tool with PDFViewCtrl through ToolManager.

By default, the signature tool does not sign with a certificate. Certificate-based signatures can be enabled using ToolManagerBuilder which will add a certificate picker and password input field to the signature UI flow.

Alternatively you can define a certificate file and password in ToolManagerBuilder. This will disable the additional signing flow for digital signatures and use the specified certificate instead.

ToolManagerBuilder tmBuilder = ToolManagerBuilder.from()
    .setUseDigitalSignature(true)
    // Optionally specify a default certificate file and password
    .setDigitalSignatureKeystorePath("my_keystore_path")
    .setDigitalSignatureKeystorePassword("my_keystore_password");
ViewerConfig.Builder builder = new ViewerConfig.Builder();
ViewerConfig config = builder
    //...
    .toolManagerBuilder(tmBuilder)
    .build();

The signed document is then saved to a separate file.