ACPL217 minimum forward voltage
Is there any risk to enable the P MOSFET if i leave the PIN 1 not
  connected ?


With pin 1 not connected there is no current into the photodiode and hence, according to the diagram you posted: -

 

V\$_{CE}\$ will be high (due to R\$_L\$) and deactivate the P channel MOSFET (assumes gate connected to V\$_{CE}\$ and source connected to V\$_{CC}\$).