I'm the lead developer of Mappt for Android.
Mappt allows you to import and export markers, lines, polygons and geotagged photos and their associated attribute data as well as view various forms of imagery from many common GIS formats, though GeoPDF is not one of them right now :)
If you could export to one of the supported imagery formats (ECW, JP2, Compact Cache, WMS and WMTS formats), you could import into Mappt.
If you require editing and capture of data and can export your data in a supported geometry format (e.g. Shapefile or KML/KMZ), then you can import it into Mappt. Users in the field can then edit the geometry and associated attribute data, then export via email, Google Drive, etc.
Mappt also allows you to create new vector layers and define attribute schema in the field.
All functionality in Mappt is available without requiring connection to any server or cloud platform. All functionality is fully available offline, including support for imagery layers.
You can trial Mappt by downloading it from the Google Play store, here. Once your trial ends, Mappt will revert to a restricted free version. See our website for the breakdown of pricing tiers.
Finally, while we don't support GeoPDFs today, @orbl_soil is correct in that we can shuffle our roadmap around based on user demand; much of Mappt's existing feature set was guided this way. Please get in touch via the live chat feature of our website (mappt.com.au) or directly via email@example.com.