If the link is directly to a pdf, like <a href=''xxx.pdf''>click here</a> it depends on the settings at the readers computer. It may either run the adobe program as a separate program, or active the adobe plugin that opens in the same window. You might be able to force the use of a new window by a link like <a href=''xxx.pdf'' target=_blank>, but that's all.
You can't control the size of the window that opens, and you certainly can't control if the text inside the windows is displayed at 50%, 100% or 140%. That's a setting inside adobe reader, and totally outside the reach of html.
I have a book excerpt I want to put on my webpage. I did it as a .pdf, but it looks too big when opened as a full page (and too small at 100% size). I think it looks best generally when the pdf at about 140% size, so ideally when people click on the excerpt link I would like a new window that would open to a specific size that will best display the pdf file. so how do i do that html code-wise? (both ''open in a new window'' and specify the size of that window?) bear in mind I am pretty basic in my coding skill and do it by hand, not with a program. thanks- fj