Chrome Version: 68.0.3437.0
OS: Chrome OS 10704.0.0 (Official build) dev-channel eve

What steps will reproduce the problem?
(1) Create PDF file in Google Drive (for example, by printing something to PDF and saving it to Google Drive).
(2) Rename the file so that it does not have the .pdf extension or for some reason I am not sure of have the file created that way to begin with.
(3) Try to open this file with the Files app on Chrome OS.

What is the expected result?
Since the file is recognized as a PDF it should open in Chrome using the built-in PDF viewer.

What happens instead?
The system offers a number of Android apps that support PDF files but it does not open with Chrome.

Renaming the file to have a .pdf extension fixes the problem. When the file is in the Downloads folder the Files app doesn't recognize it as a PDF. It seems like Google Drive remembers some MIME type information and this is why it is still tagged as a PDF despite the missing extension. The bug is that despite being recognized as a PDF in this state it still won't open with the system PDF viewer. Since Google Drive is okay with PDF files in this state Chrome OS should be able to deal with them.