If I understood your business task correctly, in this example you're trying to operate with 'Document' lookup. For this lookup can exist a lot of duplicated documents that are connected to different companies/accounts. In this situation, if you want to have distinct records and avoid seeing duplicated records in the list, you are able to merge the lookup values.
In order to do that, you just need to go to the section Lookups (in System Designer functional area), then find the lookup ‘Document’. After that click on the button ‘Actions’ and select ‘Select multiple records’. Then select the values you want to merge and select the option ‘Merge records’. After that, you will be able to choose the record you want to be kept. As a result, all duplicate records will be merged and there will be only distinct records.
More about Merging operation you can find in the following article: