It is possible to have Rainforest testers open and view PDFs provided to them in Rainforest Virtual Machines through the PDF readers preinstalled on the VM.
For all VMs that run a Windows operation system (OS) - such as Chrome HD, Firefox HD, Internet Explorer 11 HD, etc... - these VMs all have Adobe Acrobat Reader preinstalled to allow testers to open and view the PDF.
For all VMs that run an OSX OS - namely OSX Chrome (HD), OSX Firefox (HD and Safari HD - these VMs do not posses a specific program to open PDFs. However, these VMs do have the Preview desktop app preinstalled, which is capable of opening PDFs.
For Rainforest's mobile platforms, specifically the Android and iOS VMs used for mobile testing, it is the case that they don't have a preloaded application like their desktop counterparts specifically for opening PDFs. However, because the Android VMs feature a Chrome browser and the iOS VMs feature Safari, it is still possible to view PDFs as these browsers have PDF reading functionality built into them.