Hello,
Using the SignPDF class to sign PDF files, x and y options can be used to position the signature and the image content. Please check the options detailed on the API documentation page of the method (https://www.phpdocx.com/api-documentation/digital-signature-package/digitally-sign-docx-pdf-with-PHP).
This method requires using an image. A text can't be added as signature content instead of an image.
If needed you can use GD to generate an image adding a text (https://www.php.net/manual/en/function.imagestring.php), and then add the output image as the image signature with SignPDF.
Regards.