Ideally, you will want to work on the die-lines in Adobe Illustrator. For this, click and download the dieline you are looking for

I will automatically open a new window with the die-line as a PDF file. On the top right-click the download icon

Once the file is in your downloads folder, right-click > Open with > Adobe Illustrator

*Note that you will only be able to open the file in illustrator if you have Adobe Illustrator on your device.