Is it possible to export Unity3D to WebGL as one file?
I cant find any instructions how it can be done.
A Unity3D WebGL build has to be multiple files when it's exported. That's just how Unity structures it's WebGL builds. There's usually an index.html file, as well as 3 or more folders with data on the same level. The majority of the game in contained within two files called "html.data" and "html.js". Most of the other files are config files.
You can zip that entire directory into one file for ease of transport, but you cannot build a single file output.