PDF files do not open in Internet Explorer

Many users have been reporting trouble with opening links to Adobe Reader files in Internet Explorer 10 and 11: a black box with white X or “denied” icon appears instead of the linked document. The first thing is, of course, to open IE’s Tools menu (keyboard shortcut Alt+X), click Manage add-ons and verify that Adobe PDF Reader plug-in has been enabled.
You should also verify that ActiveX Filtering is not active.

Error sign in Internet Explorer 11 for PDF files

If the two above steps have been completed and linked PDF files still do not open in Internet Explorer, it is time to scream in utter horror. Or not. 😛

Launch Registry Editor by opening the Start menu and typing “regedit” (without quotes) into the search box. Click the result.
Next, expand HKEY_CURRENT_USER, Software, Microsoft, Internet Explorer and click Main. See if there is an entry titled TabProcGrowth in the right pane. If there is, its value is probably 0 (zero). Wow, you’ve located the source of all evil! 😉 Just double-click the entry and set its value to 1.

Internet Explorer TabProcGrowth value 0 prevents linked PDF files from opening in the browser

In case there is no such entry, right-click on Main, select New and click String Value.

Internet Explorer, Main. To add new string value, right-click ‘Main’ and select New.

Type TabProcGrowth (correct capitalization is required!) and press Enter key to confirm renaming.

Rename new string value to TabProcGrowth

Double-click the TabProcGrowth entry and set its value to 1 (one). Click OK.

Set the TabProcGrowth value to 1

Now close Registry Editor and all Internet Explorer windows. Click the troublesome link and see: IE does load PDF files like a champ now! Cool!

According to Microsoft, Tab Process Growth is available since Internet Explorer 8 and it sets the rate at which IE creates New Tab processes.

What else is noteworthy here:

  • the problem seems to affect 64-bit Windows 7, 8/8.1 and 10 users only;
  • there are some other 32-bit Browser Helper Objects (BHOs), Toolbars, and ActiveX controls that do not work as expected until the value of Tab Process Growth entry has been changed;
  • the TabProcGrowth entry is not always a string value (REG_SZ), it can also be a DWORD value (REG_DWORD).