Is it possible to take an Excel spreadsheet that's been developed over time into a 'darn good tool' and convert it into a protected and viable 'commercial' spreadsheet that could be sold for a nominal fee? The reason I'm asking is that a friend and former neighbor of my FIL is a professional estimator for a commercial construction company. He's apparently their top estimator and has built his own spreadsheet over the years that essentially "fills in the voids" that most estimators and available programs have (I'm paraphrasing his words). Anyway, he's talking about giving his spreadsheet away to students at the local tech school just so it provides value to someone when he retires... which his company is trying to keep him from doing because he's apparently pretty good. I told him that if it could be redesigned and or protected so that someone couldn't change formulas (or hack it easily) and hose it up he could/should consider marketing it for some retirement income, etc. Is this possible, other than just using password protection, etc? It seems to me I had a guy build a complicated series of interactive spreadsheets years ago whereby my planners could only input certain types of data into specific fields, etc... and they couldn't mess with the core program. Am I remembering correctly that this is possible to do using Excel?