Zoom to fit: PDF Embedded in HTML
Bit of a late response but I noticed that this information can be hard to find and haven't found the answer on SO, so here it is.
Try a differnt parameter #view=FitH to force it to fit in the horzontal space and also you need to start the querystring off with a # rather than an & making it:
filename.pdf#view=FitH
What I've noticed it is that this will work if adobe reader is embedded in the browser but chrome will use it's own version of the reader and won't respond in the same way. In my own case, the chrome browser zoomed to fit width by default, so no problem , but Internet Explorer needed the above parameters to ensure the link always opened the pdf page with the correct view setting.
For a full list of available parameters see this doc
EDIT: (lazy mode on)
For me this worked(I wanted to zoom in since the container of my pdf was small):
<embed src="filename.pdf#page=1&zoom=300" width="575" height="500">