!#
The line you are typing, repeated before you press Enter.
Every other event looks backward; this one looks at the line still being written. !# expands to everything typed so far.
Alone it duplicates the line, which rarely helps. With a word designator it becomes the backup trick: !#:1 repeats the first argument so you only append the suffix.
$ cp ./relatorio-final.pdf !#:1.bak
cp ./relatorio-final.pdf ./relatorio-final.pdf.bak