Opening PDF Using subprocess.Popen Failing

[Laura Creighton]

I think that your problem is that you have Protected Mode enabled.
If you do, you either have to disable that, or write a policy config
file.

https://www.adobe.com/devnet-docs/acrobatetk/tools/AppSec/protectedmode.html

says.
From: Policy configuration

Protected mode prevents a number of actions which IT can bypass by
creating a white list of allowed actions. The component that reads
these policies is called a “broker.” The broker performs actions based
on those policies, and when an admin provides a properly configured
policy file, the broker can bypass the application’s default
restrictions.

The broker first reads and applies all custom policies prior to
applying the default policies. Since custom policies take precedence,
they are useful for fixing broken workflows, supporting third party
plug-ins, and cases where unsupported machine configurations cause the
Protected Mode to impair required functionality.

Configurable policies have two requirements:

    They must reside in the Reader install directory adjacent to
        AcroRd32.exe in the install folder. for example: D:\Program
        Files (x86)\Adobe\Reader 10.0\Reader\ The name of the policy
        file must be ProtectedModeWhitelistConfig.txt.

So, well, I don't have a windows machine.  I cannot test this any more
for you, alas.

Laura