Attachments vs Associated Files: What is the difference?

Simply put, Attachments are files added directly to a Project.  This is most commonly done by going to Project > Files > Add Attachment.  Associated Files are files that were added to a specific record.

Files also get added within a module such as Estimate, Bill, Expense, Change Order, and so on.  Any file that that was added to one of these modules, will appear within the Project as an Associated file.  Meaning, it is a file linked to the Project but associated with another module.

Limitations

Because the Associated File was added to another record (such as an Expense), it cannot be deleted from the Project > Files tab.  Instead, it has to be deleted from the source.  That prevents the accidental deletion of a file that doesn’t look important, but may be necessary for a particular record.

Original Source

To easily find the transaction where the file was originally used, view the attachment details and click View Original Location.  Clicking this will open the record in a new tab.