Hello carmelab67870876
Sorry for the delay in response to your query and apologize for the inconvenience caused. As per the description above, you are not able to sign a PDF file as the signature field is not selectable, Is that correct?
Please check the PDF properties from File>Properties>Security and check is the signing is allowed for the PDF?
You can sign out and sign back in with your current Adobe ID and password in Acrobat or Reader and see if this brings any difference.
Are you using Adobe Acrobat or the free desktop version of Adobe Reader to sign the PDF file? Have you tried signing any other PDF file and check if the issue is reproducible?
Let us know how it goes.
Regards,
Anand Sri.