Simple AutoHotkey script disables and enables touchpad on Windows 10. Synaptics touchpad driver must be installed. This is targeted at older machines where the driver is installed, but Function key for disabling the touchpad doesn’t work.

synapticshotkey.ahk

;Disable and Enable Synaptics touchpad using Keyboard Shortcut on Windows 10

;CTRL+F9 to enable the Synaptics Touchpad
^F9::
Run C:\Windows\System32\control.exe main.cpl ;Open Mouse Properties
Sleep 1000 ;Wait one second
if WinExist("Mouse Properties") { 
    WinActivate ;Make Mouse Properties the active Window
    Send, ^+{TAB} ;Go to last tab
    Send, !E ;Alt+E to enable touchpad
    Send, {ENTER} ;Enter to confirm and close window
}

;SHIFT+F9 to disable the Synaptics Touchpad
+F9::
Run C:\Windows\System32\control.exe main.cpl ;Open Mouse Properties
Sleep 1000 ;Wait one second
if WinExist("Mouse Properties") {
    WinActivate ;Make Mouse Properties the active Window
    Send, ^+{TAB} ;Go to last tab
    Send, !D ;Alt+D to disable touchpad
    Send, {ENTER} ;Enter to confirm disable
    Send, {ENTER} ;Enter to confirm and close window
}