(Electronic) Vanishing Ink

We've all heard of vanishing ink. There was a time when banks wouldn't allow one to use one's own pen. There is another kind of vanishing ink: electronic vanishing ink. Not long ago, I downloaded an agreement, signed it, and sent it. Today, I wanted to look at the agreement. It had expired, electronically. The file was on my computer, and so was a backup, but they were dud. OBSERVATION: However, I had followed the advice I give here: save agreements in another format before you submit them. I still have it in Portable Network Graphic format.