In mobile browser tap plus symbol to open new tab.
Beside the plus symbol in the toolbar is a square box with a number inside: the opened tabs.
Tap/click the square box, you should view a small picture of all the open tabs. Select the one with audio from this site.
In the open tab with audio, begin playback. Then click the open tab for the pdf images.
Click on box with number again when you want to stop audio, select the open tab with audio, and use the playback controls.