Defect in Adobe PDF Embed API when using pen on touch screen notebook

My web application is running on a touch screen laptop with a pen (MPP 2.0). 

It uses Adobe PDF Embed API to view and make annotations to a PDF.

However, it is unable to use pen to select text (use pen to point at the text on the screen but the text CANNOT be selected), and therefore resulted in unable to make highlight, underline or strikethrough by pen. 

But it is OK to use finger to select text.

It is OK to use pen to select text if the PDF is directly opened in browser (NOT embeded in Adobe PDF Embed API).

It is OK to use pen to select text if the PDF is opened in Adobe Acrobat Reader.

It is OK to use pen to add comment and make free-hand writing in Adobe PDF Embed API

Is it a defect of Adobe PDF Embed API when using pen on touch screen laptop?