In general, there is a way to restart frozen apps, and of needed, restart a frozen iPad, and fix other issues in general. If you need something other than what I post here, please, do ask me, as I am very good with iOS devices.
Also, everything I post here is comparable for all iOS devices(iPad, iPhone, iPod Touch).
Closing and restarting an app:
1. Exit the app
2. Double tap the home button
3. Press and hold the issue app, in your case, HTML Presenter
4. Tap the red "-" button(no, this does not uninstall the app, it just closes it)
5. Reopen the app
Restarting a frozen or slow iPad:
I suggest you do this every month just because it removes excess data.
1. Press and hold the power button and home button until you see the apple logo
2. Continue off from where you were.
Forcing a restore upon iPad:
1. PRAY you have been a loyal "backer-uper" and backed up before said crash
2. Plug iPad into computer
3. Press and hold the power button and home button until 1 second after the screen goes black
4. Release ONLY the power button
5. Keep holding the home button until you see Windows say "Installing Device Driver" or something along those lines(sorry Mac users, I don't know what the response would be for a Mac)
6. You can THEN AND ONLY THEN release the home button
* * * --> The next step may take up to five minutes to occur <-- * * *
7A. If your computer opens up iTunes, Jesus heard your prayers, just restore from your most recent backup
7B. If your computer did not open up iTunes, you may need to bring your iPad to an Apple store.
Remember, if something confuses you, or you have a different issue, please reply as I am one to thoroughly explain how to solve the issue.