We are having this issue only when a PC is connected to VLAN using a static IP. The following are the summaries:
When a PDF file is accessed from IE, Adobe Reader plug-in takes a long pause before the Reader is launched
This long delay happens while accessing a PDF file on the web. Accessing files saved on a local or network drive is not affected by this
This problem also occurs when link to a PDF file is accessed from Adobe Reader (not the add-in, but the Reader itself)
This problem can be fixed by disabling the IE integration of Adobe Reader (disable "Display PDF in browser" option)