PDF Files will not open in Internet Explorer 1. Press Windows Key + R combination, type put Regedt32.exe in Run dialog box and hit Enter to open the Registry Editor.

Internet Explorer also supported the once-popular ActiveX plug-ins, which enabled it to open types of files not normally supported by browsers. Many old sites relied on ActiveX in order to function.

In case you're one of the people who's been trying to open a PDF via Internet Explorer 11 to no avail, fear not: Microsoft heard you and has addressed the problem with its KB5004760 update.