Implement undo and redo feature for annotations

Hi,
I am implementing Undo and Redo functionality for annotations, I am able to implement undo functionality using annot.RemoveFromPage() API.
My problem is that how can I implement Redo functionality.

You need to implement it yourself by keeping track of the annotations info (pageno, rect, ...)
You can save this info in a database if you want.

Can you please provide some information on what are the necessary parameters to be kept to redo an annotation.
for example:
for text highlight what details are required?
for text underline what details are required?
for ink what details are required?

Same parameters needed to create a new annotation
www.androidpdf.mobi/documentation/javado....html#AddAnnotMarkup (int, int, int)
[], int)
www.androidpdf.mobi/documentation/javado...(com.radaee.pdf.Ink)

Ok, then How can I get Matrix of an annotation?

it depends how you created them in the first place, you can save the info while adding the annotation, at this moment all the info are available