A shared form template can be filled per recipient from a database and each personalized PDF e-mailed out.

Read rows, fill the form, export and send.
using var connection = new MySqlConnection(connectionString);
connection.Open();

using var reader = new MySqlCommand("SELECT Name, Email FROM Recipients", connection).ExecuteReader();
while (reader.Read())
{
    var form = new StiForm();
    form.Load("Forms/Invitation.pdf");
    // set the form's fields from the row, then export to PDF
    var pdfBytes = form.ExportToByteArray(new StiPdfFormExportSettings());

    var mail = new MailMessage("from@company.com", reader.GetString("Email"));
    mail.Attachments.Add(new Attachment(new MemoryStream(pdfBytes), "form.pdf", MediaTypeNames.Application.Pdf));
    new SmtpClient("smtp.company.com").Send(mail);
}

How it works. One template drives many personalized documents, so a mail-merge over PDF forms runs straight from the database.