Under the "Project Accounting" tab, if it is related to a project entry or a project and WBS, you can select the project from the "Projects" window, link it with the document by sending and saving. Also, if you want to link the project's WBS, you can do the same.
If you want to associate more projects, you can select the first one, type in the % rate and save. The system will show another 2-row field to add more projects and WBS elements and show the remaining % rate to complete 100%.
To delete project records, you must check the "Delete" checkbox and click the "Delete" button.