Is it possible for a windows service to print a PDF file?

Question

I have this function within a Python script that has been installed as a windows service with NSSM. When the Python script is run normally (i.e. not as a service), the file is printed. However, when it is installed as a service it does not print.

The print command is externally triggered over opc-ua from another device.

Is it even possible to print while the script is installed as a service? While installed as a service, I don't get any exceptions either. Sometimes I got KeyboardInterrupt exception while sleeping between loops.

Is there another way to print a file triggered externally over opc-ua?

I know I could for example create 20 different triggers in Windows task scheluler, that thus would be executed every 5 seconds and check the opc-ua variable. This seems like a very tedious process

Here is a section of my Python script:

def CheckOpcuaNode(latestPDF):
    client = Client("opc.tcp://192.168.202.90:4840/")
    try:
        client.connect()
        opcuaNode = client.get_node("ns=6;s=::AsGlobalPV:g_saveParameters.bPrintNow")
        Result = opcuaNode.get_value() 
        if Result == True:
             print("print file: %s" % str(latestPDF))
             os.startfile(latestPDF, "print")
             try:
                time.sleep(4)
             except KeyboardInterrupt:  # Ignore keyborditerruption
                print("ERROR KeyboardInterrupt while printing: %s" % sys.exc_info()[0])
             opcuaNode.set_attribute(ua.AttributeIds.Value, ua.DataValue(False))
    except:
            print("ERROR while checking if PDF shall be printed: %s" % sys.exc_info()[0])
    finally:
        client.disconnect()

def LatestPdf():
    return 'path\to\PDF\file.pdf'

if __name__ == '__main__':
while True:
    latestPdfFile = LatestPdf()
    if latestPdfFile != '':
        CheckOpcuaNode(latestPdfFile) # check If PLC has asked to print pdf file
    try:
        time.sleep(4)
    except KeyboardInterrupt:  # Ignore keyborditerruption
        print("ERROR KeyboardInterrupt between loops: %s" % sys.exc_info()[0])

Answer 1

Acrobat opening a window and then proceeding to print the file is your problem.

Services generally do not have access to a graphical environment. They are typically "non-interactive".

You might want to find a command line PDF printing tool or print directly from your Python script. Programming questions are off topic here so I cannot address that particular side of the problem (it belongs at Stack Overflow).

Answer 2

1. run the service under a regular user account
2. login under that user acccount to open Adobe Reader and accept EULA (needs to be done for each user) and connect the network printer (not possible with "local system account") plus make it the default

Troubleshooting: in your script call "wmic printer list brief >> c:\serviceprinters.txt" to see if the user profile loaded correctly / network printer is available