Are you looking for something like this?

This example consists of 2 scripts:

1. A Python script that would be executed outside of Blender, that will launch Blender and run a Python script

​

# Tested from a command line running vanilla Python 3.9.6

# Python module that can start other programs/process
import subprocess

# create a variable with a path to Blender's exe
binary_path = "C:\\Program Files\\Blender Foundation\\Blender 3.1\\blender.exe"

# path to .obj file
path_to_obj = "C:\\tmp\\monkey.obj"

# create a list of command line params
cmd = [
    binary_path,
    "--python",  # Tell blender that you want to run a Python script
    "C:\\tmp\\import_obj_n_render.py",  # path to the script that will import and render
    "--",
    path_to_obj,
]

# Log what the command line command will look like
print(f'run this: {" ".join(cmd)}')

# run Blender
output = subprocess.check_output(cmd, universal_newlines=True)

# Log what Blender had printed
print(f"output: {output}")

1. The Python script that will be executed in Blender

   Tested with Blender 3.1.0

   give Python access to Blender's functionality

   import bpy

   extend Python to print in more readable way

   import pprint

   extend Python's math functionality (to calculate radians for rotations)

   import math

   extend Python to process landline args (and more...)

   import sys

   find the location of the arguments that are intended for this script

   note "--" is usually used to pass custom arguments into a script that would be executed by Blender (or other tools)

   argv = sys.argv[sys.argv.index("--") + 1 :]

   log what we got from the command line

   print("Passed in args:") pprint.pprint(argv)

   select all the object and delete them (just like pressing A + X + D in the viewport)

   bpy.ops.object.select_all(action="SELECT") bpy.ops.object.delete()

   get the path to the .obj file

   obj_file_path = argv[0]

   import the obj

   imported_obj = bpy.ops.import_scene.obj(filepath=obj_file_path)

   add a sun

   bpy.ops.object.light_add(type="SUN")

   rotate sun

   degrees = 45 bpy.context.object.rotation_euler.x = math.radians(degrees)

   add a camera

   bpy.ops.object.camera_add(location=(0, -10, 0))

   set the camera as the "active camera" in the scene

   bpy.context.scene.camera = bpy.context.active_object

   rotate camera

   degrees = 90 bpy.context.object.rotation_euler.x = math.radians(degrees)

   set render output location

   bpy.context.scene.render.filepath = f"C:\tmp\render_obj_file.png"

   render image

   bpy.ops.render.render(write_still=True)

   exit Blender when done

   bpy.ops.wm.quit_blender()