How to add electronic signatures to PDFs on Android

This guide explains how to add an electronic signature (eSignature) to a PDF document on Android using Nutrient Android SDK, both through the built-in user interface (UI) and programmatically.

Adding an electronic signature programmatically

In Nutrient Android SDK, electronic signatures are implemented as PDF annotations, commonly referred to as signature annotations.

Electronic signatures can be either ink or image annotations, created with:

• InkAnnotation for drawn signatures.

• StampAnnotation for image-based signatures.

To apply an eSignature:

1. Use setIsSignature(true) to mark the annotation as a signature.

2. Add it to the document via PdfFragment#addAnnotationToPage().

Licensing requirements for signature annotations

Creating, updating, and deleting signature annotations requires a license that includes either the Annotations component or the Electronic Signatures component. If your license includes only the Electronic Signatures component (without the Annotations component), modifications are restricted to signature annotations exclusively. Any attempt to modify non-signature ink or image annotations (isSignature = false) or other annotation types will be disallowed.

Creating an ink signature

To create an ink signature programmatically, use to the following code snippet:

val pdfFragment: PdfFragment = ...

// Create the ink annotation.
val annotation = InkAnnotation(0)

// Set the line color and width.
annotation.color = Color.RED
annotation.lineWidth = 3f

// Set the stroke data. For example, this would be loaded from end user input on another device.
// This example code is just hardcoding a stroke with three points.
val line = listOf(
    PointF(100f, 100f),
    PointF(150f, 150f),
    PointF(200f, 100f)
)
annotation.lines = listOf(line)

// Mark this ink annotation as a signature.
annotation.setIsSignature(true)

// Add it to the page.
pdfFragment?.addAnnotationToPage(annotation, false)

final PdfFragment pdfFragment = ...

// Create the ink annotation.
final InkAnnotation annotation = new InkAnnotation(0);

// Set the line color and width.
annotation.setColor(Color.RED);
annotation.setLineWidth(3f);

// Set the stroke data. For example, this would be loaded from end user input on another device.
// This example code is just hardcoding a stroke with three points.
final List<PointF> line = Arrays.asList(
    new PointF(100, 100),
    new PointF(150, 150),
    new PointF(200, 100)
);
annotation.setLines(Collections.singletonList(line));

// Mark this ink annotation as a signature.
annotation.setIsSignature(true);

// Add it to the page.
getPdfFragment().addAnnotationToPage(annotation, false);

Creating an image signature

To create an image signature programmatically, use to the following code snippet:

val pdfFragment: PdfFragment = ...
val bitmap = BitmapFactory.decodeFile("my-signature.png")

// Create the image annotation.
val annotation = StampAnnotation(0, RectF(50f, 440.0f, 500f, 0.0f), bitmap)

// Mark this image annotation as a signature.
annotation.setIsSignature(true)

// Add it to the page.
pdfFragment?.addAnnotationToPage(annotation, false)

final PdfFragment pdfFragment = ...
final Bitmap bitmap = BitmapFactory.decodeFile("my-signature.png");

// Create the image annotation.
final StampAnnotation annotation = new StampAnnotation(0,
    new RectF(100, 100, 300, 140),
    bitmap);

// Mark this image annotation as a signature.
annotation.setIsSignature(true);

// Add it to the page.
getPdfFragment().addAnnotationToPage(annotation, false);

Using the built-in UI

If you’re using the SDK with Forms, end users can initiate the signature creation modal by tapping a signature form field within the document. If no signature form field is present, end users can manually add a signature using the signature tool button.

If the Annotations component is included in your license, the signature tool is available within the annotation toolbar.

If the Annotations component is not included, the signature tool appears directly in the main toolbar by default. It can also be manually added using forceSignatureButtonPositionInMainToolbar in the PdfActivityConfiguration.Builder.

Signature creation modal view

When the signature creation modal view is displayed, end users can add a signature using one of three methods:

• Draw — End users can create a handwritten signature using a touchscreen or stylus.

• Attach an image — End users can attach an existing signature image from their device.

• Type — End users can enter their signature as text using a chosen font style.

End users can attach an existing signature image from their device. If the hardware supports it, they can also capture a photo of their handwritten signature on paper for a digital scan. This option is ideal when signing on a device with easy access to stored files.

End users can enter their name and select from a predefined set of font-based signature styles. This method ensures accessibility and is fully compatible with:

• Screen readers such as VoiceOver, TalkBack, NVDA, and JAWS.

• Assistive technologies such as Switch Control on Mac and iOS.

By default, Nutrient provides four signature styles, and you can customize the available options by defining a list of preferred fonts.

Color options

For both the Draw and Type options, end users can choose between black and two shades of blue to ensure the signature remains distinguishable from the document background.