Adobe ACROBAT READER 4.0 - MANUAL 2 Manual page 46

The browser supports PDF viewing, but the PDF file is not optimized or the
server does not support byte-serving, so the entire PDF file downloads to the
machine with the browser and then appears within the browser window.
The browser supports PDF viewing, and PDF files are embedded in an HTML
page. An ActiveX browser such as Internet Explorer supports navigating
through the document. Netscape Navigator-compatible browsers can display
the PDF document within an HTML page, but require a link to a full-window
view for navigation.
Acrobat or Acrobat Reader is configured as a helper application for the
browser, and the browser may support PDF viewing within the browser
window. The entire PDF file downloads to the machine with the browser, and
the Acrobat viewer launches as a separate application and displays the PDF
document.
See also Setting up Acrobat Reader as a helper
Adobe® Acrobat® Reader 4.0
application.
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