Aha, perhaps Nitro PDF changes some of its resource names between different versions?

@tzuk

Thanks for the suggestion. I went to the %Temp% location and, indeed, I see a "BCL Technologies" (no quotes) folder there. Interestingly enough (although probably irrelevant in this case), that folder contains two subfolders: NitroPDF5 and NitroPDF6. In any case, my OpenFilePath statement should take care of this.
Tzuk, you mentioned something interesting about NitroPDF in another thread, "Fineprint", on Oct 30, 2007. The message was related to the already present background process named: NitroPDFPrinterMonitor.exe. Does this ring a bell?

@Guest10
Thanks for new resource name. I tried it immediately but, unfortunately it did not work in my case. I am wondering the same thing tzuk is: could it be that the resource name changes at different versions of NitroPDF? In the spirit of "Teach a man to fish ...", could you, please, explain to me how did you go about figuring out what OpenWinClass resource string is?

Thanks to all of you,

1. Create a new sandbox to use for testing purposes, such as "TestBox".
Sandbox > Create New Sandbox > TestBox

2. Either use Sandbox Settings for the following, or copy/paste the lines below (2B) into the settings for the new sandbox:
2A. Sandbox Settings > Resource Access > Window Access
Click the "Edit/Add" button and put a single star (*) in the window. Click OK.
Then Resource Access > File Access > Direct Access
Click "Edit/Add" and enter
%Temp%\BCL Technologies

Click OK a couple of times, back to the Sandboxie window

or,
2B: Paste this into the new sandbox's settings using "Configure" > "Edit Configuration"

OpenWinClass=*
OpenFilePath=%Temp%\BCL Technologies

3. Click File > Resource Access Monitor
Leave open the Resource Access Monitor window.

4. Right-click the Sandboxie tray icon, hover the mouse over the new sandbox, and choose "Run Any Program"
Type in the box in the "Run Sandboxed" window:
notepad
and click OK

When Notepad opens, type some text into the Notepad window and then Print, selecting the "NitroPDF Driver".
---
Assuming you successfully print, go back to the Resource Access Monitor window and click the button to copy the text to the Clipboard.
Open Notepad, and paste the text into it from the Clipboard.
Look for a resource similar to the one shown here:



The resource shown is the one to use in your other sandboxes.
When finished with the new sandbox, just delete the contents and then you can delete the sandbox with
Sandbox > (hover over the sandbox) > Remove Sandbox
---
Having 2 subdirectories under the %Temp%\BCL Technologies folder shouldn't matter, since Sandboxie automatically assumes a wild card at the end of the line.
If you want to make sure the wild card is being used, you could add one yourself.
%Temp%\BCL Technologies*
but it should not be necessary.

Good luck.

@Guest10

Excellent and informative instructions! Many thanks! It WORKED

It's hard to tell if the WinCls string will stay the same at the next NitroPDF update but here is what works for me at version 5.5.0.16:

OpenWinClass={AD744029-AC6A-4C0C-A597-D0B02CDB4DE4}

That is, of course in conjunction with the file resource:

OpenFilePath=%Temp%\BCL Technologies

I'm a happy camper. Thanks again.

Glad to hear it worked. I wasn't going to bump this thread again, but reading your post made me realize that I didn't have the latest NitroPdf update. After installing the same version as you, your exclusion is the one that works for me now, too.
I hope they don't keep changing the resource names, because neither of these is the one that's listed on Sandboxie's "Known Conflicts" page. I don't know what version tzuk tested.

NitroPDF v5.3.1.8:
OpenWinClass={03576772-AD02-4630-BC5F-3648526FDF87}
OpenFilePath=%Temp%\BCL Technologies

NitroPDF v5.5.0.16:
OpenWinClass={AD744029-AC6A-4C0C-A597-D0B02CDB4DE4}
OpenFilePath=%Temp%\BCL Technologies

Thanks for sorting it out Guest10. I updated the Known Conflicts page with these two additions.