Since Chrome™ version 57 the old internal page chrome://plugins is replaced by new address: chrome://components
The new ("components") page does not offer enable/disable functionality. If you want to enable/disable the Flash plugin: the new home for this option is in the "Settings" menu. There is also an option to change the PDF viewer.
To change Flash plugin or PDF settings:
1) Click on the "Settings" menu:
2) Scroll down to the end of the Settings page and click "Advanced...":
3) Under "Privacy", click "Content Settings" button:
4) Scroll until you find the Flash settings:
Here you can enable/disable Flash at all or on "per-site" basis.
5) Scroll to the end of the content settings and you'll find the PDF settings: