OneNote 2016 should be able to search and find text inside attachments
As far as I can see, OneNote cannot currently find text contained inside attachments of any kind (unless I've inserted a printout of the attachment). The trouble is, though I don't always want to insert a printout, I do always want *all* my content in OneNote to be fully searchable.
Lotus Notes has had this capability for 20 years. See indexing option "Index attached files" in this support document: https://www.ibm.com/support/knowledgecenter/en/SSKTMJ_9.0.1/admin/admn_creatingandupdatingfulltextindexesforsingledataba_t.html
Thanks for always improving!