--- title: "Electronic + Digital Signing" canonical_url: "https://www.nutrient.io/guides/android/samples/electronic-digital-signing-kotlin/" md_url: "https://www.nutrient.io/guides/android/samples/electronic-digital-signing-kotlin.md" last_updated: "2026-05-15T19:10:04.916Z" description: "Combine an electronic signature created with ElectronicSignatureDialog with a certificate-based digital signature." --- # Electronic + Digital Signing Combine an electronic signature created with ElectronicSignatureDialog with a certificate-based digital signature. [Get Started](https://www.nutrient.io/sdk/android/getting-started.md) [All Samples](https://www.nutrient.io/guides/android/samples.md) [Download](https://www.nutrient.io/guides/android/downloads.md) [Launch Demo](https://www.nutrient.io/demo/) --- ```kotlin /* * Copyright © 2018-2026 PSPDFKit GmbH. All rights reserved. * * The PSPDFKit Sample applications are licensed with a modified BSD license. * Please see License for details. This notice may not be removed from this file. */ package com.pspdfkit.catalog.examples.kotlin import android.annotation.SuppressLint import android.content.Context import android.graphics.Bitmap import android.net.Uri import android.os.Bundle import android.widget.Toast import androidx.core.graphics.createBitmap import androidx.fragment.app.Fragment import androidx.fragment.app.FragmentManager import androidx.fragment.app.FragmentOnAttachListener import com.pspdfkit.catalog.R import com.pspdfkit.catalog.SdkExample import com.pspdfkit.catalog.tasks.ExtractAssetTask.extract import com.pspdfkit.configuration.activity.PdfActivityConfiguration import com.pspdfkit.forms.FormType import com.pspdfkit.forms.SignatureFormElement import com.pspdfkit.signatures.DigitalSignatureMetadata import com.pspdfkit.signatures.Signature import com.pspdfkit.signatures.SignatureAppearance import com.pspdfkit.signatures.SignatureGraphic import com.pspdfkit.signatures.SignerOptions import com.pspdfkit.signatures.SigningManager import com.pspdfkit.signatures.getPrivateKeyEntryFromP12Stream import com.pspdfkit.signatures.getX509Certificates import com.pspdfkit.signatures.listeners.OnSignaturePickedListener import com.pspdfkit.ui.PdfActivity import com.pspdfkit.ui.PdfActivityIntentBuilder import com.pspdfkit.ui.PdfFragment import com.pspdfkit.ui.signatures.ElectronicSignatureFragment import io.reactivex.rxjava3.android.schedulers.AndroidSchedulers import kotlinx.coroutines.runBlocking import java.io.File import java.io.FileOutputStream import java.io.IOException import java.security.GeneralSecurityException import java.security.KeyStore /** * Showcases how to combine a created signature annotation using the [ElectronicSignatureFragment] with digitally signing * the document using a certificate. * * See guide: https://nutrient.io/guides/android/signatures/using-electronic-signatures-and-digital-signatures-together/ */ class CombineElectronicSignaturesWithDigitalSigningExample(context: Context) : SdkExample( context, R.string.CombineElectronicSignaturesWithDigitalSigningExampleTitle, R.string.CombineElectronicSignaturesWithDigitalSigningExampleDescription, ) { override fun launchExample(context: Context, configuration: PdfActivityConfiguration.Builder) { // The form field for signing is on page with index 16. configuration.page(16) // Extract the document from the assets. extract(WELCOME_DOC, title, context) { documentFile -> val intent = PdfActivityIntentBuilder.fromUri(context, Uri.fromFile(documentFile)).configuration(configuration.build()).activityClass(CombineElectronicSignaturesWithDigitalSigningActivity::class).build() // Start the CombineElectronicSignaturesWithDigitalSigningActivity showing the demo document. context.startActivity(intent) } } } /** * Shows how to implement a signature picked listener and document signing listener in order to create a signature and sign with the * created signature render. */ class CombineElectronicSignaturesWithDigitalSigningActivity : PdfActivity(), OnSignaturePickedListener, FragmentOnAttachListener { /** Name of the previously clicked signature form field (if any). Used to access it after a configuration change. */ private var signatureFormFieldName: String? = null override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) supportFragmentManager.addFragmentOnAttachListener(this) // In case this activity is being recreated (e.g. during a configuration change), reattach // the activity as listener to the existing dialog. Calling restore() is safe, and won't do // anything in case the dialog isn't currently shown. ElectronicSignatureFragment.restore(supportFragmentManager, this) // Also restore information about any previously clicked signature for element. We'll use // this when adding an ink annotation later. if (savedInstanceState!= null) { signatureFormFieldName = savedInstanceState.getString(STATE_FORM_FIELD_NAME, null) } } /** * Intercept clicks on form elements so we can customize showing the signature picker. * * @param fragmentManager FragmentManager the fragment is now attached to. This will * be the same FragmentManager that is returned by * [Fragment.getParentFragmentManager]. * @param fragment Fragment that just received a callback to [Fragment.onAttach] */ override fun onAttachFragment(fragmentManager: FragmentManager, fragment: Fragment) { if (fragment is PdfFragment) { fragment.addOnFormElementClickedListener { formElement -> when (formElement.type) { FormType.SIGNATURE -> { val signatureFormElement = formElement as SignatureFormElement if (!signatureFormElement.isSigned) { onSignatureFormElementClicked(formElement) // By returning true, you intercept the event and prevent Nutrient from showing the signature picker itself. true } else { false } } // This click event is not interesting for us. Return false to let Nutrient handle this event. else -> { false } } } } } override fun onSaveInstanceState(outState: Bundle) { super.onSaveInstanceState(outState) // Make sure to persist information of any clicked signature form element (so it outlives configuration changes). outState.putString(STATE_FORM_FIELD_NAME, signatureFormFieldName) } /** * This callback handles showing the signature picker whenever an unsigned signature form element is clicked by the user. * We need to keep track of the form field name so we can retrieve it when digitally signing after the signature has been created * in the Electronic Signature Dialog. The dialog is opened by Nutrient automatically when the signature form element is clicked. * This behaviour can also be overridden here if required. */ private fun onSignatureFormElementClicked(formElement: SignatureFormElement) { // Keep reference of the stored signature form element so we can later on access it. signatureFormFieldName = formElement.formField.name // We need to control the showing of the signature dialog in order to attach this as a listener. ElectronicSignatureFragment.show(supportFragmentManager, this) } /** * We are the signature creation listener, so this method is called by the signature picker, * whenever the user selects/creates a signature. */ override fun onSignaturePicked(signature: Signature) { // You can add you custom signature handling logic here. //... digitallySignWithSignatureAnnotation(signature) } /** * This method is called by the signature picker, if the user dismissed the picker without selecting a signature. */ override fun onDismiss() { signatureFormFieldName = null } /** * This is an example that shows how to use the created signature annotation as the digital signature stamp appearance. * Note we're only ignoring the return of getFormFieldWithFullyQualifiedNameAsync for the sake of the example. */ @SuppressLint("CheckResult") private fun digitallySignWithSignatureAnnotation(signature: Signature) { val document = document?: return val signatureFormFieldName = this.signatureFormFieldName?: return // Retrieve the previously clicked signature form element. We do this asynchronously to not block the UI thread. document.formProvider.getFormFieldWithFullyQualifiedNameAsync(signatureFormFieldName).observeOn(AndroidSchedulers.mainThread()).subscribe { formField -> val clickedSignatureFormElement = formField.formElement as SignatureFormElement // We want to place the ink annotation on top of the signature field. We retrieve the widget annotation to access its position. val formFieldAnnotation = clickedSignatureFormElement.annotation // The signature object provides convenient conversion to ink or stamp annotation. val signatureAnnotation = signature.toAnnotation(document, formFieldAnnotation.pageIndex, formFieldAnnotation.boundingBox) // Add the annotation to the document. This step is required so we can render the signature // in order to pass the render to the `SignatureAppearance` when digitally signing in the // next step. We remove it once we have the render. // Here, we use the synchronous `AnnotationProvider` method as the next steps need to wait for this to complete. runBlocking { document.annotationProvider.addAnnotationToPage(signatureAnnotation) } val w = kotlin.math.abs(signatureAnnotation.boundingBox.width().toInt()) val h = kotlin.math.abs(signatureAnnotation.boundingBox.height().toInt()) val signatureBitmap = createBitmap(w, h, Bitmap.Config.ARGB_8888) signatureAnnotation.renderToBitmap(signatureBitmap) // Now we've made the bitmap, we can remove the annotation from the document, as it will appear on the digital // signature when we digitally sign the document. runBlocking { document.annotationProvider.removeAnnotationFromPage(signatureAnnotation) } // Now sign the document using the certificate added in the example class in `addCertificateAndSigner`. signDocumentWithSignatureBitmap(clickedSignatureFormElement, signatureBitmap) } } /** * Takes the created signature bitmap and digitally signs the document using the bitmap and the signing certificate initialised in * [CombineElectronicSignaturesWithDigitalSigningExample]. */ private fun signDocumentWithSignatureBitmap(formElement: SignatureFormElement, signatureBitmap: Bitmap) { val outputFile = File(filesDir, "signedDocument.pdf") val signatureAppearance = SignatureAppearance( showWatermark = false, signatureGraphic = SignatureGraphic.fromBitmap(getImageUri(signatureBitmap)), ) val key = getPrivateKeyEntry(this) val signedDocumentUri = Uri.fromFile(outputFile) val signerOptions = SignerOptions.Builder(formElement.formField, signedDocumentUri).setSignatureMetadata( DigitalSignatureMetadata(signatureAppearance = signatureAppearance), ).setPrivateKey(key.privateKey).setCertificates(key.getX509Certificates()).build() // handles the signing process SigningManager.signDocument( context = this, signerOptions = signerOptions, onFailure = { t -> Toast.makeText(this, t.localizedMessage, Toast.LENGTH_LONG).show() }, ) { setDocumentFromUri(signedDocumentUri, null) // Signature page. pageIndex = 16 } } /** * Stores the signature image to the FS in order to obtain a URI to pass to the [SignatureAppearance]. */ private fun getImageUri(bitmap: Bitmap): Uri { val imageFile = File(cacheDir, "signature.png") val fileStream = FileOutputStream(imageFile) bitmap.compress(Bitmap.CompressFormat.PNG, 100, fileStream) fileStream.close() return Uri.fromFile(imageFile) } @Throws(IOException::class, GeneralSecurityException::class) private fun getPrivateKeyEntry(context: Context): KeyStore.PrivateKeyEntry { // Inside a p12 we have both the certificate (or certificate chain to the root CA) and private key used for signing. val keystoreFile = context.assets.open("digital-signatures/ExampleSigner.p12") return getPrivateKeyEntryFromP12Stream(keystoreFile, "test") } } private const val STATE_FORM_FIELD_NAME = "Example.FORM_FIELD_NAME" ``` This code sample is an example that illustrates how to use our SDK. Please adapt it to your specific use case. --- ## Related pages - [Application Policy](/guides/android/samples/application-policy-kotlin.md) - [Custom Form Highlight Color](/guides/android/samples/custom-form-highlight-color-java.md) - [Custom Page Templates](/guides/android/samples/custom-page-templates-java.md) - [Digital Signature (Basic)](/guides/android/samples/digital-signature-basic-kotlin.md) - [Disabled Annotation Property](/guides/android/samples/disabled-annotation-property-java.md) - [Image Document](/guides/android/samples/image-document-kotlin.md) - [Compose Image Document](/guides/android/samples/compose-image-document-kotlin.md) - [Inline Multimedia](/guides/android/samples/inline-multimedia-kotlin.md) - [JavaScript Form Filling](/guides/android/samples/javascript-form-filling-kotlin.md) - [Overlay Visibility](/guides/android/samples/overlay-visibility-kotlin.md) - [PdfFragment](/guides/android/samples/pdffragment-kotlin.md) - [Reader View](/guides/android/samples/reader-view-kotlin.md) - 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