Main difference between forwarding and replying is that when forwarding, all attachments are also sent to sender.
There are two forms of forwarding in ProfiMail:
In this mode, message’s attachments (if any) are added as normal attachments in message composer, and original message text is used as quoted text.
When forwarding as attachment, the original message being forwarded, including all attachments, is packed into one single attachment. The attachment has name with .eml extension, and its mime-type is “message/rfc822”. Such attachment may be later opened by email clients as normal email message.
You may read long store about forwarding here: Email forwarding.