[FEATURE]: Dynamic fields insertion (signer metadata) directly in PDF

Is your feature request related to a problem? Please describe.

In many legal and administrative documents, the signature is accompanied by additional information such as:

• Full name of the signer
• Role or title
• Company or organization
• Email address
• Date of signature
• Location

Today, this information must be manually written inside the PDF before sending it for signature, which creates several issues:

• Requires editing the PDF before every signature request
• Increases risk of human error
• Makes document automation difficult
• Limits integration with structured workflows

Describe the solution you'd like

Add the ability to insert dynamic fields linked to signer metadata directly inside the PDF document when configuring a signature request.

This would allow administrators or document creators to automatically display information about the signer (such as name, company, role, etc.) inside the document without having to modify the PDF beforehand.

Describe alternatives you've considered

No response

Additional context

Introduce dynamic text fields linked to signer attributes that can be placed directly in the PDF viewer when configuring the document.

These fields would automatically populate when the signer signs the document.

Example dynamic variables
Possible variables could include:

{{signer.name}}
{{signer.firstname}}
{{signer.lastname}}
{{signer.email}}
{{signer.company}}
{{signer.role}}
{{signer.title}}
{{signer.date_signed}}

Example use case
When preparing a document for signature, the sender could place fields such as:

Signed by: {{signer.name}}
Title: {{signer.role}}
Company: {{signer.company}}
Date: {{signer.date_signed}}

The issue does not name files, tests, or entry points. Start by locating the PDF viewer's field-configuration flow and the signer metadata used during signing, then determine how dynamic variables should be stored and resolved. Done means configured signer attributes appear in the generated PDF for the requested fields.