Create a new Column using a part of an existing document name

Hi all,

I saw some similar questions , but not quite what I am looking for. I am using Sharepoint 2013 .

I have few documents (word, excell) in my document library . They all have similar names , ending by _MonthDate.

I want to be able to create another column wich will show me only this part of a string (MonthDate) according to the document name . Something like Right([columnName],8) and that use it as a filter to show my documents in this folder.

Lets say , by default I would see the latest monthdate , but will have an option to selest multiple month using a multiple choice in filter.

I cant find a way how to find a name of the document and use when creating a new column...

I also tried to create a workflow Setting a [Name] to another custom column, but the workflow doesnt do anything ...I sem to be missing something

Any suggestions ? really appreciate your help .....