Just to update the thread, LiveCycle may be end of life but it's available in form of AEM forms Designer. 6.5 designer being the latest version. Forms created in the old version are fully supported on any latest AEM form designer but yes some refactoring in terms of layout and scripting might be required to support the latest scripting engine.
The only product available to you is the one you have, but you should consider migrating. Adobe would say migrate to an Acrobat form. I'd say, migrate to HTML forms. To be clear "migrating" here means "learn a new technology and do the whole job again" not "open in a new app and have it change stuff".
You might consider also keeping a Windows 7 machine around to ensure compatibility if you do want to keep editing this file. Not saying it WON'T work on Windows 10, but it's a risk.