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How to place signature fields with Smart Anchors

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Smart Anchors are invisible placeholders you embed in PDF documents. When uploaded, Subnoto automatically detects them and creates signature blocks at those locations, eliminating the need to manually position fields via the API.

Format

Section titled “Format”

Smart Anchors follow this format:

{{ [email protected] | signature | width | height }}

Components:

  • Email: Must match an existing contact or team member (otherwise ignored)
  • Block type: Currently only signature is supported
  • Width/Height: Dimensions in PDF points (recommended: 180×60 for 3:1 ratio)

Example:

{{ [email protected] | signature | 180 | 60 }}

Critical Requirements

Section titled “Critical Requirements”

Make anchors invisible: Set the text color to match the page background exactly (e.g., white text on white background). If visible, the anchor will appear in the final document.

Email validation: The email must match an existing contact or team member in your workspace, otherwise the anchor is ignored.

Adding Smart Anchors to Your PDF

Section titled “Adding Smart Anchors to Your PDF”

  1. Open any editor (PDF editor like Adobe Acrobat, or Word editor like Google Docs, Microsoft Word, LibreOffice, etc.) - as long as it can export to PDF

  2. Add text where you want the signature block to appear

  3. Type the anchor format:

    {{ [email protected] | signature | 180 | 60 }}

    Google Doc example showing how to write a Smart Anchor

  4. Set text color to match background (white on white, etc.) to make it invisible

  5. Export or save as PDF

Testing Your Anchors

Section titled “Testing Your Anchors”

Use the Smart Anchor Preview Tool to validate anchor placement before uploading:

Smart Anchor detection in devtools

Using with the API

Section titled “Using with the API”

Enable Smart Anchor detection when uploading via the create-from-file endpoint:

Terminal window
curl -X POST https://enclave.subnoto.com/public/envelope/create-from-file \
  -H "Authorization: Bearer $ACCESS_KEY:$SECRET_KEY" \
  -F "workspaceUuid=your-workspace-uuid" \
  -F "envelopeTitle=Contract" \
  -F "[email protected]" \
  -F "detectSmartAnchors=true"
const formData = new FormData();
formData.append("workspaceUuid", "your-workspace-uuid");
formData.append("envelopeTitle", "Contract");
formData.append("file", createReadStream("document.pdf"));
formData.append("detectSmartAnchors", "true");


await fetch(`${API_BASE_URL}/public/envelope/create-from-file`, {
    method: "POST",
    headers: {
        Authorization: `Bearer ${ACCESS_KEY}:${SECRET_KEY}`,
        ...formData.getHeaders()
    },
    body: formData
});

Quick Reference

Section titled “Quick Reference”
  • A4 page size: 596×842 points
  • Recommended block size: 180×60 points (3:1 ratio)
  • Margins: Keep blocks 50-100 points from page edges
  • Multiple anchors: Can be placed on the same page or different pages
Section titled “Related Resources”