Help for About Converting Microsoft Office Documents from https://help.libreoffice.org/Common/About_Converting_Microsoft_Office_Documents should be updated so that it can be used as a reference in different bugs.
1. There's "general overview of Microsoft Office features that may cause conversion challenges" but I hope they are not all there with LO 5.3.
2. For "Opening Microsoft Office Documents That Are Protected With a Password" PowerPoint is not mentioned at all and as Bug 33538 says: "Unable to open any password-protected PPT or PPS (PPTX and PPSX work)".
Open XML should be amended: "The Office Open XML format uses 128-bit AES encryption."
Just as an update to this bug, the current page for LO 7.3 still seems to be the same as in the original report by Timur, which still was in the Wiki format.
The relevant help page now is: