The option to "add" attachments to an existing pdf "now" not available

Hard Drive on ASUS laptop replaced

Operating system upgraded to Windows 10

Reinstalled Adobe Acrobat X Standard

Downloaded Acrobat Reader DC

And, new operating system had Adobe Acrobat Distiller X already on it

Before the hard drive replacement, was able to create PDF's and, using the "Add Attachment" option in the left side menu of the PDF form, browse the C-drive and select files to be attached to the PDF.

Now, after the new hard drive and the re-loading of the above software, when opening a previously created PDF containing attachments; the attachments appear in the left side of the PDF form but the option to "Open attachments"  (add new attachments) is grayed out and not functional.

The option to "open attachments" previously enabled browsing the C-drive to locate files to attach to the PDF.

Not sure what has to be done to enable the option to add attachments to an existing pdf form

Any suggestions will be appreciated