Question : how to select the last 4 characters in the right of a column

I have a column in a SQL server table that stores file paths. The amount of characters varies for each row. The data is something like this: [E:\Documents\Form.pdf].

I need to figure how how many different file formats are in this table..is there a way to substring (col,1,4) to right, not the left?

Answer : how to select the last 4 characters in the right of a column

Right(col, 4)