The user would expect a pdf viewer to be in fullscreen mode. To achieve this goal but still keeping the functionality that is provided in the pdf viewer page I would propose to replace the bottom navigation with a floating action button
THe bottom navigation is removed. Now there is a FAB that opens e menu where the user can choose to search the pdf or edit the tags related to the document.
The user would expect a pdf viewer to be in fullscreen mode. To achieve this goal but still keeping the functionality that is provided in the pdf viewer page I would propose to replace the bottom navigation with a floating action button