right click application won't open
In Finder, I right click on a PDF and choice Open with PDFpenPro. I get a window that says "The application "PDFpenPro" can't be opened." If I go down to Other, I can open the application.
Where probably is a solution on this forum, but it is difficult to find it.
Thanks for help.
I am running the latest OS X and an up-to-date PDFpenPro
iMac with Retina 5K display, macOS Sierra (10.12.3)