Every document can be linked to various other documents in OneOfficeERP.
The 'Links' tool gives you an option to check if the current document is linked to any previous documents and lists down all the forward links.
To do so, you can simply go to the menu and click on 'Links'. A Pop-Up box will open which will list down all the documents that this document has been linked to.
Note: This option will only show you the forward links in a document; the backward links can be found within the document itself.
E.g., if you want to check, which Sales Invoices are linked to your Sales Order, you can check the 'Links' from the dropdown menu. However, the information about the Quotation with which this Sales Order has been linked shall be present within the Document itself.