LibreOffice was capable for handling PDF signatures since 2016 already. There have been recent improvements in the past year, namely creating visible PDF signatures and reworking the underlying PDF signature verification functionality to use PDFium for tokenization. This means that PDF signature verification (which happens implicitly, during opening any PDF files) now uses much more battle-tested code to provide this feature. Come and see how this work is implemented, where are the still rough edges and how you can help.