This is still a problem in 2021.

But you don't have to retype your whole signature manually. Once the email is generated, just go to the Outlook ribbon and navigate: Include>Signature>[select signature].

Not automatic, but at least somewhat easy.

Hi,
Thanks for your response!
Please take a note that currently this is not possible to insert signature when using Attach to Email by Adobe directly.
For attaching to email, other applications use MAPI process of Microsoft and this is the limitation of Mapi that it does not allow insertion of already created signatures in the Outlook.
To verify this you can test it with any word file and attach the word file by the steps:
1. Open any word file
2. Goto "File>>Share>>Email>>Send as Attachment" (See the snapshot attached)
3. Verify the draft email does not insert your signature, please update us in caseyou see different behavior.

Regards,
Arvind

In e-mail accounts, such as Yahoo and Outlook, users can set up multiple signatures for the bottom of their e-mails depending on which e-mail address the e-mail is being sent from. It would be wonderful to be able to set up a signature at the bottom of an e-mail when sending a PDF attachment.

For example, I send e-mails with statements and invoices every month. I have to retype my signature, company name, address, phone and fax numbers and website address every time I send the e-mail.

Hi,
I think you are talking about inserting your signature in the draft email whenever you attach a PDF by email button on it. Is that the case?
It is as design, Adobe Acrobat does not insert signature automatically if it was the concern.

Could you please check this behavior with other types of files like notepad/word/excel.
Kindly follow the steps-
-Right click on any notepad/word file
-Select "Send to->Mail recipient" --> draft email window opens with attachment.

After the above steps, draft email opens which does not inset signature automatically.
Kindly let us know if you need more info.

Regards,
Arvind