Trying to understand what the code is doing.
See if this helps any...
Range("A1", Cells(Rows.Count, "A").End(xlUp))
----------------------------------------------------------
Finds last data cell in Column A
Dn.Font.Bold
-------------------
Dn is the cell being iterated in the above range and we are going to assign the expression below to its Font.Bold property
For Each Dn In Range("A1", Cells(Rows.Count, "A").End(xlUp))
-------------------------------------------------------------------------
Iterates each cell in the range A1 down to the last cell in Column A
Not " " & Dn & " " Like "*##[A-Za-z][A-Za-z] *" And
Not Dn & " " Like "*## *" And
Dn Like "*#*"
-----------------------------------------------------------------------------------------------------------------
Contains three logical expressions (highlighted in red, blue and green) that all must be true (hence, the And operators) in order to return True to the above Font.Bold property of the cell currently being iterated in the For..Next loop. Like is a logical operator in VB and what it does is compare the text to the left of it to a text pattern made up of wildcards (? and *) and character groups (what is inside square brackets).
Not " " & Dn & " " Like "*##[A-Za-z][A-Za-z] *"
--------------------------------------------------------
Here I concatenate spaces in front of (which is actually not required for how I code this logical expression) and behind (this is required to handle the case when nothing number/letters come at the end of the text) the value in the currently being iterated cell and then test this against the pattern which looks for the
negative (important that you remember that) of the pattern formed by zero or more characters followed by a mandatory two digits followed by two mandatory upper or lower case letters followed by a mandatory space followed by zero or more characters. This will return True for any text that does
NOT contain two digits followed by two letters somewhere in the text.
Not Dn & " " Like "*## *"
--------------------------------
Here I concatenate as space onto the back of the currently being iterated cell (for the same reason as in the above description) and then test it against the pattern which looks for the
negative (again, important that you remember this) of the pattern formed by zero or more characters followed by two mandatory digits followed by a mandatory space followed by zero or more characters. This will return True for text contains two digits followed by any thing other than a space.
Dn Like "*#*"
----------------------
This returns True if the text in the cell being iterated contains at least one digit.
