Case
The issue we are running into is when an attachment is added to an opportunity it is not being shared with the account. And anything that goes into an opportunity needs to be reflected in the corresponding account.
Solution
There is no out-of-the-box logic that would copy the attachment from the Opportunity to the correspondent account. If there is a custom functionality added to do that, please provide us with its name and the full description of how it should work.
Otherwise, to achieve the aim, you need to create a custom business process that would be triggered every time the attachment is added to the opportunity, would read the notes and the account from it and add the attachment to the account. Thus, the process would consist of three elements:
1)Start signal
2)Read Data
3)Modify Data