Why can't I delete the annotations in the pdf file.

[Loc Zhang (上杉夏香)]

Here is my logic:

1.I use FPDFPage_GetAnnotCount to get count annotations of an page

2.traversal every annotation

3.I use FPDFPage_RemoveAnnot to remove but I get some errors <could not remove annotation>

I want to know why?

This is my original: annot_test-quark.pdf

This is my result: