Run:

    ngspice -b pd1.cir

This will generate the operating point file 'Pre-Pin-Diode-OP.0.d1', which
is read as the ic.file (initial condition file) for 'pindiode.cir'.
Note that if there is no output line in the .model section of 'pd1.cir',
the generated file will be named 'OP.0.d1'. In this case the ic.file value
in 'pindiode.cir' would need to be changed to match it.

Then:

    ngspice -b pindiode.cir

can be run which will input 'Pre-Pin-Diode-OP.0.d1'. If you do not run
'pd1.cir' first, the 'pindiode.cir' simulation will run OK but tell you it
cannot find the iinitial condition file.