TOPIC:

if you are developing on android, there is a listener with callback method:
OnPDFAnnotTapped();
it implement on high level(PDFViewController class in Demo project).
in this method you can call m_view.PDFPerformAnnot(), this call will return callback:
OnPDFOpenURI();
this callback tells uri address user tapped.

and you can set customer uri on PDF Editor for some customer operation.

You shall interact with document contents after a single or double tap:

In pseudo-code you shall:
i=ObjsGetCharIndex(tap_x, tap_y)
start=ObjsAlignWord(i, -1)
end=ObjsAlignWord(i, 1)
string=ObjsGetString(start,end)

Then you should apply a regex to string and evaluate if it's a proper URI syntax.

You shall add pagee.ObjsStart();
just after Page pagee = m_doc.GetPage(0);

I've a doubt about x, y in your code.
Which is the value you're loading in the variables?
Are you losing touch coordinates, isn't it?

i tested following codes, and it works:
m_annot_pos = m_layout.vGetPos((int) event.getX(), (int) event.getY());
m_annot_page = m_layout.vGetPage(m_annot_pos.pageno);
Page page = m_doc.GetPage(m_annot_page.GetPageNo());
page.ObjsStart();
int ichar = page.ObjsGetCharIndex(new float[]{m_annot_pos.x, m_annot_pos.y});
int start = page.ObjsAlignWord(ichar, -1);
int end = page.ObjsAlignWord(ichar, 1);
String result = page.ObjsGetString(start, end);
Log.e("TAP", result + " " + ichar + " " + start + " " + end);

if not work yet. it maybe following issue:
1.you have not active any license, even demo license.
2.the PDF page is pure image page, the text is pixel image, not fonts.

if red watermark displayed on page, it mean, you have not actived demo license.
this mostly because you have changed package name.

if blue watermark displayed, i think your PDF file is pure image page.

the attachment is the PDF file i test, acturally, it works on every PDF file.