.pdf , .epub , .mp4 , or .mobi are generally standard for media files.

Secret Junior Acrobat Vol. 4: The 16L Update

: Note any specific quality improvements or new additions included in this "updated" version compared to any earlier releases of Volume 4.

"Vol 4" is common in manga or comic series, though no "Secret Junior Acrobat" is currently indexed in major databases.

If you are looking for specific content, here are a few common areas where similar naming conventions appear: