eReceipts are stored in PDF format in NetCommunity database.
There are three ways to give your donors access the eReceipts.
Donors will need to login to the Blackbaud NetCommunity site to view the eReceipt if they were logged in when they made their donation.
Donors will not need to login to the Blackbaud NetCommunity site to view the eReceipt if they were not logged in when they made their donation.

1) Insert eReceipt Download URL merge field in the body of Acknowledgement Email for donation form part. To insert the field, edit the donation part and edit the Acknowledgement Email.
2) Insert eReceipt Download URL merge field in custom confirmation screen in donation form part. Custom confirmation screen is available under Payment section when you editing the donation form part.

If you need to resend the eReceipts to donors, you can retrieve the eReceipts pdf going to the specific gift record in Raiser's Edge.  Look at gift attribute: NetCommunity eReceipt URL.  Use the URL to download or save the pdf document locally.