you're very welcome.

you mean the whole column? that's not advisable. an xlsx file means you would have 1 million rows of formulas. if your formula is in B2 & you want to copy the formula until where your data stops,
1. click on B2
2. hover the cursor until it is at the bottom right of the selected cell. you should see a black cross. do a left mouse double-click

if you want to prepare some additional rows of formulas but don't want "0000" to show up when it's a blank, try:
=IF(A2="","",A2&TEXT(COUNTIF(A$2:A2,A2),"0000"))

please mark the thread as Solved if opening question is answered. thanks
=)