SP3 Pen disabled in some Excel files

[LarzStarz]

I'm a developer working on an Excel based application with a document level customization using C# and Visual Studio 2013. I want to be able to use the SP3 pen while doing product demos, but for some reason when my app is open in Excel, the Pen and writing options on the INK TOOLS ribbon tab are disabled. This is not the case when I start a new document in Excel. Any ideas why Excel would disable these tools? Thanks.

 

[nipponham]

Is it a protected file from a third party, or one that you've created yourself? Inking is not disabled by default and is working fine on new and previously created documents.