In the resources' folder, there are two files corresponding to each attached file in the notes

Today, while attempting to delete unused attached files in the resources' folder, I discovered that there are two files for every attached file in the notes.
One corresponds to the image or PDF file attached to the note, and the second one has the same name but with a .crypted extension. Is this a standard behavior? Means, when deleting a note, It is necessary to delete both files relate to a note, or this second file is an unexpected result, possibly due to a synchronization error or a bug?"