You are free to give any name to a newly created document. The only requirement is that the name can be coded in UTF-8. But it will be more convenient to give your documents names that describe what their function is and show what kind of document they are. This will be helpful when you are searching the database for the exact document to be referenced in another document.

One suggestion is to always start the name of a document with a reference to the project it belongs to. This way all documents dedicated to a special project can easily be found. Another suggestion is to include into the name a reference to the document type. E.g. a content document that belongs to the project 'MyProject' might be called 'MP cd HomePage'. I.e, this document belongs to the project MP, it is a content document and its (descriptive) name is HomePage.
Documents that will be used over and over again might be stored in a folder COMMON. E.g. a style document for displaying text as bold might be called 'COMMON vis bold'. This document does not belong to a specific project, it is used for visualization (it is a style document) and its (descriptive) name is bold.