Adding visible digital signatures to a PDF document

Use visible digital signatures to combine visual signoff with cryptographic integrity.

Common use cases include:

• Contract signing workflows
• Document approval systems
• Authenticated signoff pipelines
• Branded signature appearances

Unlike invisible signatures, visible signatures render a signature area on the page using text or images.

How Nutrient helps

Nutrient Python SDK handles signature field operations, appearance rendering, and cryptographic signing.

The SDK handles:

• Signature field dictionaries and appearance streams
• PKCS#12 certificate loading and key extraction
• Appearance customization and font rendering
• Byte range calculations and signing internals

Complete implementation

This example adds a visible signature field and signs it with different appearance options:

from nutrient_sdk import Document, PdfEditor, Signature, Color
from nutrient_sdk import DigitalSignatureOptions, SignatureAppearance, TimestampConfiguration
from nutrient_sdk import SignatureHashAlgorithm

Creating a signature field

Create a signature field at the target location before signing.

In this sample:

• The document opens in a context manager(opens in a new tab).
• The field name is ApprovalSignature.
• The position is (100, 700).
• The size is 200 × 50.

The field acts as the visible placeholder for the signed appearance:

with Document.open("input.pdf") as document:
    editor = PdfEditor.edit(document)
    page = editor.page_collection.first

    signature_field = editor.form_field_collection.add_signature_field(
        name="ApprovalSignature",
        page=page,
        x=100.0,
        y=700.0,
        width=200.0,
        height=50.0
    )

    editor.save_as("output_document_with_field.pdf")
    editor.close()

Signing with auto-generated appearance

Sign the field with metadata-driven text.

In this sample:

• DigitalSignatureOptions sets certificate and signer metadata.
• Document.open("output_document_with_field.pdf") opens the PDF before signing.
• use_auto_generated_text = True uses signer metadata in the appearance.
• show_validation_mark = True adds a validation indicator.
• sign_field(document, output_path, field_name, options, appearance) signs "ApprovalSignature".

with Signature() as signer, Document.open("output_document_with_field.pdf") as document:
    options = DigitalSignatureOptions()
    options.certificate_path = "certificate.pfx"
    options.certificate_password = "Nutrient answers all your document needs"
    options.signer_name = "John Doe"
    options.reason = "Final Approval"
    options.location = "New York"

    appearance = SignatureAppearance()
    appearance.use_auto_generated_text = True
    appearance.show_validation_mark = True

    signer.sign_field(
        document,
        "output_signed_visible.pdf",
        "ApprovalSignature",
        options,
        appearance
    )

Signing with a custom image

Use an image-based appearance for handwritten signatures or logos.

In this sample:

• Document.open("output_document_with_field.pdf") opens the PDF before signing.
• image_path points to the signature image file.
• The image renders inside field bounds.
• show_validation_mark = True keeps the validation indicator visible.
• sign_field(document, output_path, field_name, options, appearance) applies the digital signature.

with Signature() as signer, Document.open("output_document_with_field.pdf") as document:
    options = DigitalSignatureOptions()
    options.certificate_path = "certificate.pfx"
    options.certificate_password = "Nutrient answers all your document needs"
    options.signer_name = "Jane Smith"
    options.reason = "Review Complete"

    appearance = SignatureAppearance()
    appearance.image_path = "input_signature.jpg"
    appearance.show_validation_mark = True

    signer.sign_field(
        document,
        "output_signed_with_image.pdf",
        "ApprovalSignature",
        options,
        appearance
    )

Signing with custom text

Use custom text when you need workflow-specific signature content.

In this sample:

• Document.open("output_document_with_field.pdf") opens the PDF before signing.
• use_auto_generated_text = False disables metadata-generated text.
• text defines the visible signature content.
• \n creates multiline output.
• sign_field(document, output_path, field_name, options, appearance) applies the digital signature.

with Signature() as signer, Document.open("output_document_with_field.pdf") as document:
    options = DigitalSignatureOptions()
    options.certificate_path = "certificate.pfx"
    options.certificate_password = "Nutrient answers all your document needs"
    options.signer_name = "Manager"

    appearance = SignatureAppearance()
    appearance.use_auto_generated_text = False
    appearance.text = "Approved by Management\nDate: 2024-01-15"

    signer.sign_field(
        document,
        "output_signed_custom_text.pdf",
        "ApprovalSignature",
        options,
        appearance
    )

Customizing text appearance

Customize typography to match document or brand requirements.

In this sample:

• Document.open("output_document_with_field.pdf") opens the PDF before signing.
• font_name sets the typeface.
• font_size sets text size.
• text_color sets ARGB color values.
• sign_field(document, output_path, field_name, options, appearance) applies the digital signature.

with Signature() as signer, Document.open("output_document_with_field.pdf") as document:
    options = DigitalSignatureOptions()
    options.certificate_path = "certificate.pfx"
    options.certificate_password = "Nutrient answers all your document needs"
    options.signer_name = "Executive"

    appearance = SignatureAppearance()
    appearance.use_auto_generated_text = False
    appearance.text = "Approved by Executive Board"
    appearance.font_name = "Times New Roman"
    appearance.font_size = 14.0
    appearance.text_color = Color.from_argb(255, 0, 0, 128)  # Navy blue

    signer.sign_field(
        document,
        "output_signed_styled_text.pdf",
        "ApprovalSignature",
        options,
        appearance
    )

Conclusion

Use this workflow to add visible digital signatures:

1. Open the document using a context manager(opens in a new tab) for automatic resource cleanup.
2. Create an editor and access the page collection.
3. Add a signature field at specified coordinates with defined dimensions (e.g. 100, 700, 200×50 points).
4. The signature field creates a rectangular placeholder for the signature appearance.
5. Sign the field using Signature with certificate credentials (PKCS#12 format).
6. Configure signing metadata, including signer name, reason, and location.
7. Create the signature appearance with auto-generated text (use_auto_generated_text = True) to display metadata.
8. Add validation marks (show_validation_mark = True) to indicate signature validity.
9. Use custom images via the image_path property for handwritten signatures or company logos.
10. Use custom text with use_auto_generated_text = False and multiline formatting for workflow-specific approvals.
11. Customize typography with font_name, font_size, and text_color properties using ARGB values.
12. Save the signed document with visible signature appearance and cryptographic integrity.

For related signing workflows, refer to the Python SDK guides.