Adobe Acrobat "These characters cannot be used in a file name"

You type in a path and file name into Acrobat, you get this:





Apparently, this is because Acrobat is too "stupid" to append the ".pdf" to your information.

For example, if you type "C:\Temp\MyPDF", you get the error.

If you type "C:\Temp\MyPDF.pdf" instead, no error.

Am I the only one who thinks this is stupid?