How I can be sure that we are able to read an .docx document in about 100 years? I have a large collection of documents on my hard drive (including letters, cv's and other stuff). I want them to be readable and accessible for the near future (10 years), but if it is possible, up to 100 years!
Which format would be advisable?
There are 3 aspects to this:
To ensure the data survives, copy it multiple times, to multiple things (USB drive, DVD, cloud, etc). Run a file comparison program such as diff to check that the copying process worked properly. Media degraded over time, so periodically create new copies.
To ensure software exists, use standard formats such as PDF. Every time you change your computer, make sure you still can open and read the files. If you can’t, talk to whoever produced the old software to get it running on the new computer. Depending on how different the old and new systems are, this could be expensive. However, this also takes care of ensuring that hardware exists to run the software.
I keep all of my files as pdfs with txt backups. Both formats are available on Mac/Windows/Linux, and txt files are future-proof (though pdfs are neater).
When it comes to compatibility, the simpler the better. I'd like to offer two suggestions.
Store your documents as plain text. Formats like MS Word's *.docx, or Adobe's *.pdf, add formatting and a lot of additional information instead of simply storing the letters that make up the document. That's how you get centered text, tables, different fonts, bold/italic/underline, etc. Plain text files just store the ASCII (numeric) codes for all of the characters in your documents - all the letters, numbers, visible symbols, spaces, and line breaks. If you're using a PC, files of this format commonly use *.txt and are viewable in the Notepad application.
Store your documents as bitmap images. This will take a LOT of space, but it is incredibly simple and universal. Bitmap images are simply large grids of numbers. Each point on the grid contains a number from 0-255, which represents the color of that pixel in the final image. So the idea is to "take a picture" of your text documents and save it in the bitmap format. (Note that this idea is not practical in the short term at all. The files will be huge, and you won't be able to search them for text. However, in a hundred years, if a computer finds a bitmap image file, I would bet all the money I have that the computer will have a program that could display it.)
I would not trust PDF. It is a complex format that seems simple only because Adobe made reader software for multiple operating systems. (Other companies have now made reader software.) It would be wise to save multiple formats of each file. One format should be plain text. There is no formatting, other than spaces, tabs, and returns. The second part is the physical form. Good paper has held up for hundreds of years. But NASA has warehouses of tapes from early moon missions and no reader, or even the specs for a reader. Standard USB is on the way out. Computers don't come with floppy drives, and CD/DVD drives are rare. I expect standard USB thumb drives to be usable for another 10 years, at most. There is no way to store digital information that will not require monitoring to be sure it is still valid. If the medium is becoming obsolete, it can be copied to something new. By the way, this is a topic of interest to librarians.
