Have you made any changes to the computer prior to the issue?
I would suggest you to run the Internet Explorer in no add-ons mode and check if issue persists:
To open Internet Explorer in no add-ons mode,
a. Click the Start button.
b. Click All Programs.
c. Click Accessories.
d. Click System Tools, and then click Internet Explorer (No Add-ons).
Refer: Tips for solving problems when Internet Explorer crashes or stops working
Disclaimer: The Reset Internet Explorer Settings feature might reset security settings or privacy settings that you added to the list of Trusted Sites. The Reset Internet Explorer Settings feature might also reset parental control settings. We recommend that you note these sites before you use the Reset Internet Explorer Settings feature
You can also try the steps from the link and check if it helps:
Internet Explorer stops responding, stops working, or restarts
Configure Adobe to open PDF directly from Adobe reader and not from browser
To do so:
a. Open Adobe
b. Go to Edit>Preferences
c. Select Internet and uncheck Display PDF in Browser.
d. Also uncheck “Allow Fast Web View” and click OK to accept the changes.
Refer: Can't view PDF on the web