graphics state

I want to position text at some specific place in the document. However, I cannot figure out where to find the origin of the coordinate system of the page. What is the coordinate of the bottom left corner, top right corner, bottom right corner, top left corner? Where is this origin?
Example written in the context of the question How to create a PDF with a Cartesian grid?
Could anyone please provide me a sample program that can dynamically create a grid or even dots starting at (0,0) at bottom left corner on a PDF of page size "Letter" (max X = 8.5 Inches; max Y = 11 Inches)?
I'm creating a PDF where I add some text to each page as well as 2 lines. On one specific page, there's a table where I change the background color of a cell. I now get the cell with the background color I specified (grey), but the lines also change from black to grey.
I am using absolute positioning when writing text in a PDF document using iTextSharp. It only have a single BaseFont instance for a regular font and there is no Bold version of that font. I read in a post that this was an alternative way to set the font to bold: change the rendering mode and the line width. That works, but creates another problem. I don't know how to set these parameters back to my old default (non-bolded font).
I am getting the following error when I want to print a PDF generated with iTextSharp" "An error exists on this page. Acrobat may not display the page correctly. please contact the person who created the pdf document to correct the problem" The document prints fine, but why do I get this error?
I want to set the text alignment to justified, but I don't want iText to add any extra space between the characters. I prefer space between words.
Is it possible to add a watermark that will be transparent on top of an image?
This example was written in answer to the question How to add a map with a pointer to a PDF?