It could be a couple of reasons:
Different versions of Adobe or Outlook: Does your co-worker have Adobe Reader, and you have Adobe Acrobat?
Different settings in Outlook or Adobe.
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PDFEmail.net doesn't require 3rd party e-mail software such as OUTLOOK.
PDFEmail.net works with Adobe Reader users.
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http://www.nk-inc.com/support/
Try the online demo:
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