Using "this.external" throws "InvalidGetError" when file is digitally signed

[AzuresSkye]

Hey guys, I've got a bit of a weird bug that is driving me completely insane.

I have a form that checks if PDF is being opened in something other than Acrobat using "if(this.external){"

Until recently, this worked perfectly. If the form was opened in Chrome or something else, an error would pop up and the form fields would stay hidden.

However, sometime between July and now, this stopped working, but only when the forms are digitally signed.

Reproduction:

1) Document-level script executes "if(this.external){//unhide form fields}" on document open.

2) User fills form and uses digital signature field to sign.

3) User emails form to my team.

4) My team opens the form and "//unhide form fields" doesn't execute, with this error in the console:

"InvalidGetError: Get not possible, invalid or unknown.

Doc.external:3:Document-Level:zOpenDoc"

In my testing, I found that removing the "this.external" check would also result in an error when the script got to the "this.delay = true" line, however "this.dirty = false" works fine.

I'm beyond frustrated and confused dealing with this. Is this a genuine bug with Acrobat or is this a coding error on my part?

I would greatly appreciate any help that points me in the right direction.

[try67]

You need to ask the developers of the Chrome PDF plugin... It has nothing to do with Adobe.

[AzuresSkye]

Apologies for being unclear.

The issue is happening in Adobe Acrobat  Professional DC version 21.005.20060

Chrome is the reason that I need the code. 

[Bernd Alheit]

Does you get the error when you open the form in Adobe Acrobat?

[try67]

Also, post your full code, please.

[AzuresSkye]

if(this.external){
    app.alert({
        cMsg: "This form does not work in your chosen PDF viewer. Please use Adobe Reader or Adobe Acrobat.",
        nIcon: 0,
        nType: 0,
        cTitle: "Bad PDF Viewer"});
} else { //Unlock the Status field and process
    this.delay = true;

    actionSetVis("Show"); //Function that adjusts visibility of form fields

    getField("Status").readonly = false;
    switchStatus();
    if(getField("Admin.Customize") == null & & getField("Admin.Save") != null){this.removeField("Admin.Save");}
    this.delay = false;
    this.dirty = false;
};

Here's the code in the script zDocOpen. It should execute on document open. When digitally signed, it fails. 

[try67]

What's throwing the error is not the usage of the external property. It's you trying to change the visibility of fields, which is not allowed in a signed document.

[AzuresSkye]

I just tested that and that does not seem to be the case.
The attached file unhides a field On Open and then hides again On Save. Signed or not, it does not appear to throw any errors. 

[try67]

If you don't lock the fields with the signature then you can edit them, yes, but your code does a bunch of other things, too, and one of them might not be allowed...

[AzuresSkye]

Additional note: Changing "this.external" to "false" causes a different error:

GeneralError: Operation failed.
Doc.delay:10:Document-Level:zDocOpen

Which is related to the "this.delay = true"

[try67]

You can't set the external property as false. It's a read-only property.

[AzuresSkye]

Let me rephrase. In the above code, if you remove "this.external" and replace it with "false" so it skips the IF statement, then you get the error listed.