ant = page:CreateTextAnnot(rect, text, encoder)
page:CreateTextAnnot() creates a new text annotation object for the page.
The rect parameter must be a table which contains left, top, right, and bottom fields that describe
a rectangle.
Nil, the default encoding is used#HPDF_INVALID_PAGE - An invalid page handle was set.
#HPDF_FAILED_TO_ALLOC_MEM - Memory allocation failed.
#HPDF_INVALID_ENCODER - An invalid encoder handle is specified.