other files in \inst\doc

I would like to include a Mathematica notebook and cdf file (both are
ASCII files) in the \inst\doc directory as supporting documentation. These
files are not large, about 340K each one. When I check using
R CMD check --as-cran ...
I get the following warning:

......................
* checking data for ASCII and uncompressed saves ... OK
 WARNING
'qpdf' is needed for checks on size reduction of PDFs
* checking examples ... OK
* checking PDF version of manual ... OK

WARNING: There was 1 warning.

This warning disappears when I delete \inst\doc

Is this a bug?
Is it forbidden to include such ASCII files?

Regards, Ian McLeod