[BioC] warning if pdf of vignette is missing

[Manuela Hummel]

Hello,

I am working on building a package under Windows. Everything works well; 
only if I do not provide the pdf version of the vignette in the 
'inst/doc' directory I get the following warning when running Rcmd check:

* checking package vignettes in 'inst/doc' ... WARNING
Package vignettes without corresponding PDF

Also then the pdf is not built with Rcmd build.
I have seen on the daily check results page of the development packages 
that many packages get this warning.
How can I avoid this warning or can I ignore it? Or do I have to provide 
the pdf (which is not recommended)?

Thank you very much
Best regards
Manuela Hummel