accessibility toolbars and PDFs

There was a query about meeting WCAG standards.  

 Diksha.gov.in also meets WCAG standards.
All websites provide accessibility tool bar consisting of:
1) Font size increase of text
2) Dark mode or contrast.
Moodle version 4 also provides this if enabled.

On Diksha, it is found that both the tools do not work on PDFs and PPTs and only  work on other content on website. What could be the reason for this?

Copy-pasting from my reply, 

The toolbars usually used on websites generally use javascript to modify the display of HTML content by the web browser (like Chrome, Firefox, etc). PDF, PPT and other content are not displayed on the screen by the web browser directly, but instead depend on other software like PDF plugins, Microsoft Office etc. Therefore, the toolbars will only work with HTML content.

If the Userway widget works with PDF and PPT , it would be because they use some other technique for changing the display.