easy to implement customer overlay and text selection?

[Shi Yan]

hello,

I want to implement a social pdf reader where multiple users can annotate on a pdf file.

To achieve it, I want to implement a custom overlay on top of a rendered page. 

Is this easily doable with pdfium?

The annotations need to be anchored to a piece of text, how to achieve that?

I need to implement text selection / text highlighting, and the selected text need to be able to generate a signature and tied to an annotation.

When an annotation is loaded, I need to locate the corresponding text based on the signature somehow.

Is there an example code I can look at?

Thanks