Here’s an example of how a PDF plugin works–go to dashboard, select “plugin” and search for “pdf”. Find a plugin that has a lot of stars and a lot of users (that way you have a sense that the plugin is reliable), and then select and “activate”. After you’ve activated a plugin, it will show up as an option in your post panels. (alongside image/paragraph etc.)
Select “insert pdf” then navigate to the pdf on your device. It will upload into the gallery in the same way images do.
Here iis an example of a pdf i uploaded this way:Blind-Contour-Conditions