Here is my AutoHotkey script that provides a workaround to the "before you print" nonsense. Some additional improvements to function keys are also provided here. In most installations, you would need to change "Send ^+p" to "Send ^p".
; ----------------------------
; Nitro Pro
; ----------------------------
#IfWinActive ahk_exe NitroPDF.exe
; The following commands swap the CTRL-O and CTRL-SHIFT-O functions,
; so that CTRL-O provides a standard "File open" dialog window.
^o::Send ^+o ; CTRL-O = Open document
^+o::Send ^o ; CTRL-SHIFT-O = Open recent document
^p:: ; CTRL-P = Print
; This routine focuses Nitro Pro on the "Print" button in the print dialog.
; The user may then either press the ENTER key or click the left mouse button to print.
printButton = Button10 ; This is Nitro's control name for the print button. It might change in future versions of Nitro.
SoundBeep, 1000, 40 ; Play a short sound to confirm that the user has pressed CTRL-P.
Send ^+p ; Activate print dialog. This can be changed to whatever hotkey Nitro Pro uses to print.
Sleep, 1200
ControlGetPos, x, y, w, h, ScrollBar1 ; Get the position and dimensions of the scrollbar in the print dialog.
MouseMove, % x+w/2-3, % y+h-45 ; Move to bottom of scrollbar.
Sleep, 200
Click ; Navigate to bottom of print dialog window.
ControlFocus, %printButton% ; Focus on "Print" button. This enables ENTER to activate printing.
ControlGetPos, x, y, w, h, %printButton% ; Get the position and dimensions of the print button.
MouseMove, % x+w/2, % y+h/2 ; Move cursor to the middle of the "Print" button. This enables a left mouse click to activate printing.
Return
F2::SendEvent ^{F1} ; F2 = Toggle the menu ribbon.
F3::Send ^{F2} ; F3 = Hand
F10:: ; F10 = Add comment (note)
SendEvent !r
Sleep, 300
SendEvent n
Return
F12::Send ^+s ; F12 = Save as
#IfWinActive ; end NitroPDF block