The following items may be missing from the context (right-click) menu when multiple items are selected in Windows Explorer.
The following registry value may be modified to choose the number of files that may be selected while maintaining the context menu options.
Name : MultipleInvokePromptMinimum
Type : DWORD
Default : 15 (decimal)
The registry change will go into effect after logging off and back on, or after terminating Windows Explorer (Explorer.exe) and re-launching the process.
Note: a value of 16 is interpreted as "unlimited" for showing the options from the context menu, however it does not allow the actual opening of the documents selected if selecting more than 16. To allow the opening of more than 16 documents, set this key to a decimal value greater than the amount of documents you wish to open. Microsoft recommends only increasing this value to a reasonable number in a controlled environment and only where users really need this value increased.