A file or folder name starting with '.' ("dot" or "period") is considered hidden on most operating systems. By naming a file starting with '.', you accidentally hid the file and made it inaccessible to all iOS apps.
I'd highly recommend using '_' ("underscore") in the future.
We have already made the change to the new Acrobat DC for iOS app (version 15.0.x) so that it disallows the rename operation with '.' as the first character. (I assume that you are using Adobe Reader for iOS on iOS 7 or older iOS version.)
To recover your hidden file, you need to use a Windows or Mac desktop/laptop computer, install a File Manager app (e.g. iExplorer free demo version, iFunBox), connect your iPad, browse the file system on your iPad, and rename the file back to something else (so that it becomes "visible" again).
The exact steps vary depending on the File Manager app you choose. You may be able to find How-To videos on the software manufacturer's web site or YouTube.
Don't worry. Your hidden file is not permanently lost. You just need to recover it. Good luck!
That makes sense. Thank you so much! I will give it a try.