From The Inquirer:
"The main question at the start of our project was which format to save the texts. We needed to make sure [people] could still read the digital files in 50 years' time." Ammenti explained that, in order for the manuscripts to be readable, the Vatican Library opted for open source tools that do not require proprietary platforms, such as Microsoft Office, to be read.
Ammenti goes on to explain that the Vatican has chosen to use the FITS image format in order to preserve digitized scans of manuscripts and other works for decades, hopefully centuries, into the future.
See past post on OSC: Vatican Secret Archive is Digitizing to Open FITS Format.