The chrome://plugins or about://plugins page which lets you manage plugins installed in Chrome browser has been removed by Google in Chrome 57. You can still able to enable or disable Flash by visiting Content Settings (Do remember, starting from Chrome 55, HTML5 has been made default experience, Flash was blocked by default). Chromium team has provided a way to open PDFs in an external PDF viewer in Settings.
chrome://plugins page removed
When you attempt to visit the plugins page in version 57, you’ll receive this error : ‘ This site can’t be reached. The web page at chrome://plugins/ might be temporarily down or it may have moved permanently to new address. ERR_INVALDI_URL’.
After this change, here is the status of the plugins such Flash, PDF and CDM right now.
Wildwine Content Decryption Module will be always enabled.
Manage Flash or PDF Viewer plugins in content Settings
Flash or PDF Viewer plugin settings have been moved to content settings.
Visit the material transformed Settings page, search for content in the search box, scroll down until you noticed the highlighted item typed in the search box and double click on content settings.
You can see Flash and PDF document settings.
PDF documents content setting allows user to open PDFs using a different application, when that’s enabled, means Chrome Internal PDF Viewer has been disabled.
UPDATE: Here is current, content Settings of Chrome (non-material)
If user disables Flash or PDF Viewer in previous version Chrome 56, those settings will be preserved and they will still be disabled in Chrome 57 as he upgrades which has plugins page deprecated.
The bug – Deprecate chrome://plugins reveals the rationale behind the move
Objective: Remove the chrome://plugins page, moving configuration for the last remaining plugin,
Flash Player, to it’s own explicit place in content settings (including an option, in settings, to disable).
Rationale: This change should make the controls for Flash Player more discoverable, in settings (i.e. most users probably know what Flash is, but not what a “plugin” is), and will consolidate modes related to Flash Player (e.g. Plugin Power Savings mode), into a single location.
Supporting Rationale: Since we’ve deprecated NPAPI, Flash Player is now our last remaining plugin (i.e. 3rd party binary modules). Those remaining “plugins” (PDF, CDM, etc…) started life as 3rd party code, but have since been built and maintained by Google… and at this point are effectively just specialized libraries for Chrome.