The problem
Converting docx/odt files to PDF does not support drop-down lists in the initial file. The pdf file contains empty areas instead of dropdown list values.

Steps to reproduce
Use Unoconv or Google Drive file converter. (haven't tried with other onverters)
In an assignment submit a docx or odt file with drop-down lists inside. (as a student)
Open the submission for grading. (as a teacher)

Expectations
Conversion to a PDF file should not lose data, including drop-down lists values.