We advise:

• Word and OpenOffice: Although these are now based on XML, we do not currently recommend you use these formats. Please save your texts as PDF/A-1a or PDF/A-2a.
• Unformatted text (e.g. *.txt.): Can easily be preserved. The best option for this is unicode with UTF-8 encoding.
• LaTeX: Can generally be preserved. However, packages can be critical. You should ensure that your files are well documented.

Saving as PDF/A-1b in Word 2016: File > Save as > Choose PDF as the file type and select PDF/A under Options. This will save the file as PDF/A-1b. You will need additional software for other PDF types. We'll happily advise you on this.