Hi Kevin

Unfortunately I don't know the reason for not allowing pdf embedding over other file types as i am not a security expert .

I was reporting the feature in 13 to prevent this in and why this was added that was described in the feature ticket.

As far as i understand there are filters to ensure malicious code isn't able to be included in files - there may be something different about how this is stored in PDF files.

i will try and get someone with more security knowledge to provide details on the security risk . I don't think it is extreme risk otherwise there probably wouldn't be an option to allow the embedding. 

Regards