If for a human, whether the document is original or scanned, there is no problem of interpretation … for a robot, like that of Google, it is much more difficult: a scanned document is in most cases viewed in the same way as an image. Google has just taken a step forward in the understanding and classification of scanned documents…

Scanned documents difficult to analyze by engines…
Until now Google has rarely included PDF documents in its search results because their interpretation is imprecise, it could not be on the content present in these documents. The few PDF documents present did not have a snippet (description in the engine results), today Google has managed to better analyze these documents …

… Now analyzed by Google
Google is now able to analyze scanned documents using its OCR (Optical Character Recognition) technology, which converts thousands of words from image to text. These words once put into text can be indexed and classified by the engine. Google can therefore now easily classify a scanned document and display an adequate snippet.

Some examples…
Google gives some examples of research showing PDFs in the results… These examples are English, I let you go and see them on the post of the official google blog.