How do I add text and other content to an existing PDF page?

Q: I need to position different text runs to different positions on a
single PDF page. These blocks of text should be centered on a page in
vertical direction and the space between them has to be equal for all
blocks.
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A: Using PDFNet SDK (http://www.pdftron.com/net) you can add new
content to existing PDF pages. As a starting point you may want to
take a look at the following FAQ:
  http://www.pdftron.com/net/faq.html#how_watermark

and the following Knowledge Base articles:

"What is the proper way to add new content to an existing (rotated/
cropped) PDF page? "
http://groups.google.com/group/pdfnet-sdk/browse_thread/thread/10190611076bd2cd

"How can I stamp all PDF pages with a rotated and centered text
stamp?"
http://groups.google.com/group/pdfnet-sdk/browse_thread/thread/d017db32b85c78e9/8f66636628202344

The following article covers how to add center and right justified
text:

"How can I align/justify text when placing it on a page?"
http://groups.google.com/group/pdfnet-sdk/browse_thread/thread/a167e41e41ff94d2/956cc4c533b952ef