R create reference manual with R CMD check

I am writing an R package and would like to make a pdf reference manual of all functions in the package. I understood from here that R CMD check automatically creates a reference manual.

Here I read that a manual entry is created "of the functions you listed in the export section of NAMESPACE".

My NAMESPACE file looks as follows:

# Export all names
exportPattern(".")

# Import all packages listed as Imports or Depends
import(
  LIM
)

so I thought everything will be exported. During R CMD check on the package directory, at the very end it says:

 * checking PDF version of manual ... OK

However, I do not find a reference manual in my package directory (I would assume it would be in inst/doc). What am I missing here?