Search does not mark pdf-files

[Bdy 0]

My Environment is Windows 10 with Evernote 5.9.9.9915 Premium

My problem:

I frequently receive multiple PDf files and .doc documents referring to the same subject per email. If those documents refer to the exact same topic, I store them in one Evernote notebook via copy and paste. If I search for one item that is part of one of the PDF or .doc attachments, Evernote does show the associated note very quickly. If the term is part of a .doc document, Evernote marks the .doc attachment in yellow. If the term is part of a PDF file, it is not marked. In this case, I have to open alle PDF documents to find the term.

Am I doing something wrong, or is there a difference between the search result for a PDF file and a .doc file? If this is true, is there any chance that this will be changed?

Thank you very much. 

Regards,

Ulf Bernardy