I followed the K2 JavaScript Service Provider tutorials (https://community.nintex.com/t5/Technical-Issues/K2-JavaScript-Service-Provider-Preview/ta-p/125931) and was able to successfully upload a file to box.com. I've been reusing this working code to integrate with Adobe Sign but failing with NO_FILE_CONTENT error. The code snippet below seems to be the issue.
var form = new FormData();
// get file name
form.append("File-Name", properties["file1"].filename);
// get file content
form.append("File", properties["file1"].content);