pdf = application from unidentified developer?

I just figured it out!!!!

Right click on the file;

"Get Info;"

Scroll to "open with;"

Drop down menu to choose the app.

I changed from Preview to PDF Pen. Working without issue now.

Apple is the worst in everything.

I have this exact same problem...three years later and on a difference OS version (Sierra).

I took it to the Genius Bar and they claim this is a bug in Sierra. If this is truly a bug, it's been going on a looooong time.

We clearly can't be the only people with this issue. Have you been able to fix it?

This sorted the problem that I was having:

I installed Adobe Acrobat Pro for Mac, which led to pdf files being opened by default by this new program. I wanted to change that back to Preview, so I right clicked a pdf file and selected open with and then other..., but I was then getting the first error message shown by the OP. I did what scalia4114 said to do and it fixed the problem and I no longer get those error messages, which were preventing me from opening pdf files with Preview.

If you go to System Preferences -> Security & Privacy -> General where the "Allow apps downloaded from" setting is at, it will show when an app was blocked from opening a document and it gives you the OP's error.

From that setting, you can click "Allow Anyway" to solve this problem. Nothing else needs to be done than that.

Another workaround is to simply open the document from within the application, but that's a pain.

And, a reply like "Apple is the worst in everything" is simply NOT helpful to anyone. I'm sitting here trying to deal with this simple little problem while my Windows 10 PC has spent over 20 minutes trying to log in after an update, making Microsoft and Windows 10 the "worst in everything" since it's unusable. However, that kind of thinking doesn't solve either problem.

I had the same problem... fixed it by following this: http://www.cultofmac.com/241165/how-to-change-the-default-app-for-specific-files -or-file-types-os-x-tips/

This could also have been done by visiting the Security & Privacy System Preference. However, while this fixed the issue on a document by document basis, you will have to do this for every PDF you want to open permanently with a non-default app. It is as if OS X is treating each file as an app in its own right and is not particularly convenient. In my case I want PDF Expert to be the app that opens some of my files (mainly to preserve annotation formatting - yes folks, it's not universal) while keeping preview.app as the default. OS X can see that the PDF was created by PDF Expert and exactly when, so does anyone know if there is a way to set yourself up as the developer within the PDF application of choice so that OS X knows its you that created the file?

I gave up in the end and associated all PDFs with PDF Expert.

Sorry...and click "change all."

Hope that helps!

Yes, you fixed it byassociating the file type with another app, but you therefore did not have the same problem as the OP and me.