The Document Codes are types of documents that clients use as standard in all their projects. They do not represent "each" document.
Some of the most common Document Codes are: 
From above example you can use "LST" document code for the Vendor Document List and for the Spare Parts List. Same for "PRO" doc code, that can be used for all kind of Test Procedures like the Hydrostatic Test Procedure, PMI Procedure, Painting Procedure, etc.
With this Code List we build the Card List, which will show “each” document:
In the Card List (same as in an Excel file), has to be indicated the Title of each document and the document numbers. DocBoss supports several document number columns, which include internal number, customer number, end user number and sub-supplier number.
If you only have a list of documents from your customer without any code list, click here to see the best options to set up your Card List.
Check out the steps to upload a Code List in our video Add Customer to DocBoss and the article Add Doc Codes to a project. And to easily create a Card List, check out our article about levels.