Automatic Email Manager can forward the email and attachment(s) merged in a single PDF.

First add the action to 'Save and merge ...', set the desire folder and file (for example: c:\%EMAIL_FROM% %FILENAME_FULL%) and keep this folder and filename for later use.

When done add a new action 'Forward email', and set the option to 'Attach a file', in the field 'File' use the same value you set in previous action: c:\%EMAIL_FROM% %FILENAME_FULL%

It should work as expected.

See it in this video tutorial: