First convert the .ZIP file into base64. You can use a tool like https://base64.guru/converter/encode/file You cannot paste a file into a Scratch project. However, a code exists called Base64 which can turn the data of any file into a long line of text which you can paste. This project reads and decodes the binary data (1s and 0s) directly from the Base64 text, meaning that it can go at the same speed regardless of the size of the ZIP file. SB3 FILES ARE SECRETLY ZIP. You can view the contents of a scratch project file in this project as you would a zip file. It will contain the text file project.json which stores all of the Scratch code. Yes, that does mean I could use this to make a Scratch project that runs real Scratch projects. Thanks to the Julia project at https://github.com/GunnarFarneback/Inflate.jl/ for inspiring my INFLATE (decompression) algorithm. I feel like I should mention https://scratch.mit.edu/projects/418046248/ as I saw it included an INFLATE algorithm before I finished mine, however I did not use any code or implementations from it.