Hi EmilyCa.
Attaching files is a great way to keep track of anything associated with that transaction to later pull up. I can help go over how they are attached and how to link them again.
QuickBooks Desktop allows you to attach multiple files to a transaction to help keep everything organized. When you attach the file to a transaction it's actually saved into an attachments folder located in the same folder your company file is. This is why when you upgrade QuickBooks Desktop or restore a back up those files don't show up. This is due to the company file not having a link to the attachment folder like the original. In order to restore this link you'd need to repair it by going to: Company>Documents>Repair Attached Document Links. This will cause a pop up to show up that you'll need to follow the steps provided in it to select the attach folder and then click repair link.
If the attachment folder is no longer there and was not saved or copied then the only way to get the attachments back would be to attach them to the transactions again.
If you have any further questions feel free to reach back out and we'd be happy to help!
