cookie105 wrote:
How to correct this error message from popping up? The file eventually opens but the error messages occurs randomly all day. I don't know if it is only pdf files or other applications too.
I don't have adobe on my computer so I am not sure why most documents are saving with the extension pdf. I try to remove all extensions from showing in the settings but it won't remove the extension on the pdf files.
https://discussions.apple.com/content/attachment/6dd52621-24d3-443e-b513-dae7bc6c8244
every file has an extension— whether you choose to have them visible are not.
Portable Document Files (PDF) are extremely common, and can be open in Preview.app and others including Adobe Read per your example.
I can not explain your error— if it is a problem file delete it, or try duplicating it, or download a new one from the source.
You can also highlight the file and Command i will open the info pane— you can change what is the default application to open that file type

You can from Terminal drag and drop a file onto the Terminal.app window after you type file followed by a space, followed by your drag and drop... for example:
file YourFileHere
maybe or maybe not is there going to be useful information for some insight...
MacBook-Pro ~ % file BeginnersGuideToMakingMobileApps.pdf
/Users/username/Desktop/BeginnersGuideToMakingMobileApps.pdf: PDF document, version 1.3
MacBook-Pro ~ %