Help

Hi there

Hope you are doing well and thanks for reaching out.

Would you mind sharing more details to better understand the situation at your end?

Would you mind defining 'Open Acrobat file on an email'?
Are you trying to attach the PDF file to the email, or has someone emailed you the PDF file, and you are trying to open it directly from the email? To open a PDF attached to an email, simply open the email and double-click the PDF icon. for more information please check the help page: (https://adobe.ly/48EnGlt)

As mentioned you have 'forgotten the username and password'
Is the PDF file you are trying to open is password-protected and asking for the document open password? If yes, Adobe doesn't keep a hold of the user's passwords; the best way is to ask for an unprotected copy of the document from the sender, or you may try to recreate a new copy of the PDF from the original source file.

If you have forgotten the account login password: please take a look at the steps suggested here  (https://adobe.ly/4f7FA2w)
Note: Login ID is your email ID you have used for registering with Adobe.

~Amal