No serial number on box, sleeves, or discs.

I have Adobe Premiere Elements 15 and have been using the program for a couple years now. I recently got a new computer and wanted to install it on there. For the past while I've been using it on the old computer, but I don't know how, because when I went to install it on the new one it asked for a serial number. I've searched all over the box, both discs for Mac and Windows and their sleeves, and I've got no numbers listed as "serial" or that are even 24 digits. The only hint I have is a sticker on the front which reads "Theft protected: Follow instructions inside to access the serial number." There are no instructions of this sort, only a card telling me I can download with the disc or from the site. Any help would be great because my old computer is really annoying to use.