Hello,
You can add attachment in the email but it will be fixed attachment.
If you want dynamic attachment, it requires a special add-on or custom development.
Regarding the "product files" ; the HikaShop email does contains the download links as long as you configure the order statuses accordingly.
HikaShop also do have a "download" listing available in the customer front-end panel.
Afterwards, you can still perform some email overrides to add some text in your emails.
To add explanations for your customers.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.