The way you've phrased your question, it doesn't sound like you even want to edit the file with perl. Instead you're just asking how to copy it, which can be done with...

perl -ne 'print' original.html >duplicate.html
[download]

...as well as about a thousand other ways. Of course, the simplest way to do something like this is to skip perl completely and use your OS's copy command, then open up the duplicate and edit away.