(I’m just some guy not CH) I just tried using Microsoft Edge 38.14393.1066.0 / Win 10 Home 14393.1358 - it seems to work for me (trying several different documents). For example I accessed the CH Beta site and tried as an example:
Company number SC294759, filing history entry for 21 Jul 2015 (accounts):
This will open something like (may change for different accesses?):
That PDF opens OK in Edge.
Edge settings are: don’t block cookies, block popups. IE is apparently not using plug-ins for PDFs etc. I’m behind a firewall.
There has been a particular issue (corrupt XREF block) with particular PDF files but there was a fix for that quite some time ago. Someone did query that a while later however so maybe have a look at those investigations to start:
http://forum.aws.chdev.org/t/pdf-compliance-issue-inc-rendering-in-firefox/109
http://forum.aws.chdev.org/t/many-ar01-annual-returns-pdfs-are-internally-bad-corrupt/310