How to change Macro so it searches cell in excel that is selected to open PDF

I have a macro that will open a PDF in a specified location on my directory.

Currently I need to enter the document number in cell L1 and then run the macro.. how would I change this so it searches the document number that is selected on excel spread sheet? so for example if I had a reference in cell A2 as long as I highlight that in excel with the cursor.. it will open that file.

here is the code I'm using at the moment...

Sub PO_Lookup()

MyPath = "C:\Program Files (x86)\Adobe\Acrobat Reader DC\Reader\AcroRd32.exe"
MyFile = "F:\AP\POs\" & Range("L1") & ".pdf"
Shell MyPath & " " & MyFile, vbNormalFocus

End Sub

Thx for your help..