Replace text in PDF is not working

I want to replace specific text in whole pfd but it replaces only four occurrence in pdf.
I m install Aspose.pdf package from Manage NuGet package.
Can u provide me something for demo.

@shravan_sumitra

Please note that evaluation version of the API can only process four elements of any collection e.g. TextFragments, Pages, Paragraphs, Annotations, etc. In order to use API without any limitation, you should apply license before making any calls to API methods. You can get 30-days free temporary license in case you do not have one to evaluate API without any limitation. In case you still face any issue, please let us know.