Projects created in Scratch 3 are saved as .SB3 files. This file format was developed on MIT (Massachusetts Institute of Technology) for programming learning software. Scratch projects can be of the form of a stroy, animation, or simple game and is saved as a ZIP archive.
In files with the .SB2 extension, data packets containing serial numbers used by the SerialBox web application are stored. These packets can be used to unlock other companies' software protected by serial keys, however, such actions are generally against the law.
After converting the file to the new format, you will be able to use other programs to support it. Keep in mind, however, that the SB3 file after converting to SB2 may differ slightly from the original. The most important information should be kept, but if you want the file after conversion from SB3 to SB2 to be the same, you have to do this carefully and choose the proper application from the list below.
There is no guarantee, of course, that the conversion will come up to all your expectations, but it will certainly help you. If, after all, the effect of converting SB3 to SB2 does not meet your expectations, you can simply try to find on the Internet a different version of your file in SB3 format, properly converted to a SB2 file by someone else. If this fails, use the information provided in the further part of the website.
Unfortunately, if after performing the two previously described steps (trying to find your SB3 file converted by someone else, and the attempt to convert it to SB2 on your own) you still have a problem with your file, then there are only a few solutions left. You can once again try to find and install an application that can open the SB3 file in its original format (without conversion to SB2 file). Such a solution will be difficult to implement, but it certainly will give the best result.