Editable grid

In an editable grid you can populate a grid cell with a File Upload Field.  The document(s) uploaded in that grid column, as usual, won't actually be uploaded to the target Appian folder until the form is submitted - until that, they are unavailable to be targeted by most system functions like document(), etc.

Can you share a bit more about what you're hoping to accomplish, at a high level?  When you say "display document name", what in particular are you hoping to have happen that isn't accomplished by the filename being displayed within the File Upload Field, which is what already happens?

A general principle in software engineering is to not store any value that can be derived at run-time (unless there's a compelling performance-related reason to do so). The same applies here - if you CDT currently has an attribute that holds the documentId you can derive the document name from that value using a function:

docs.appian.com/.../fnc_scripting_document.html