The Studio One 3 Reference Manual is comprised of web pages so you can easily copy the contents to read it on any device or system except maybe an iPad which may reject the *.htm extender.
1. In Studio One go to Help > Open Settings Folder
2. Open the Extensions folder there.
3. Locate the file presonus.studioone3.en.help and on OS X right click and Show Package Contents or on Windows unzip it to see the contents.
4. Copy the Help folder and put it on any other system or device and open the main file StudioOne3ReferenceManual.htm in the sub folder to view it.
Additionally, a user appears to have converted the 3.5.0 manual to PDF unofficially here: https://daw.one/presonus-studio-one-3-reference-manual-in-pdf-unofficial/