I am trying to find a relationship between the zoom factor in PDFView,
and what other products consider 100%. Interestingly Adobe Reader and
MSWord show different sizes for 100%. However, to get PDFTron to
display documents the same size I need to put in quite unusual
numbers, such as 1.37 to match MSWord 100%, or 1.565 (I think) to
match Adobe Reader 100%. I just wonder if you could steer me towards
any information that will help me make sense of these numbers.
The behavior for 100% zoom is typically application specific. When it
comes to PDF, at 100% the size of the page on the screen should
roughly correspond to the actual dimensions of the physical page.
PDF format is using units called points (where one point is 1/72 of an
inch). At the time the initial PDF specification was written, the
default screen resolution was 72 DPI, and as a result, the viewer
didn't have to scale the page when rendering at 100%. These days
typical monitor is using 96DPI or higher and you would need to scale
up the page in order to match the display resolution.
You would need to obtain the monitor DPI using platform specific call
(e.g. using GetDeviceCaps() Win32 API) and then multiply the initial
zoom in PDFView with the following ratio: (monitor DPI)/72.0.