Outdated documentation
The latest documentation was moved to docs.qfield.org
To use an existing project as Base Map, do a long press on the project and check “Base Map Project”.
QField is able to use vector data and raster data without a QGIS project.
It is possible to open directly vector data. For example below with a GPKG:
It is also possible to open directly raster data. For example below with a TIF: