google is your friend, in the first 3 hits I found ...
Powerpoint Viewer Mac powerpoint viewer mac download powerpoint viewer mac free powerpoint viewer 2007 powerpoint viewer powerpoint viewer and many more programs powerpoint viewer for mac microsoft. A Guide to Installing a Microsoft Powerpoint Viewer on My Mac img source: brighthub.com. PowerPoint Viewer for Mac img source: brighthub.com. Experience the best of Office with the latest versions of Word, Excel, PowerPoint, and more.
Here is a tutorial and link to viewer for 2013:
http://www.powerpoint-2013-tutorials.com/powerpoint-2013-viewer/
Here is the viewer up to 2010, you probably already have it:
https://www.microsoft.com/en-us/download/details.aspx?id=13
Sway. I've only played with it briefly. I've looked at several quick tutorial youtubes. I don't think 'file size' is an issue for a couple of reasons.
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First, the app is entirely web based. You provide a link to the cloud source of the presentation. You don't need Office to run sway, just a browser on any size device, from 7' smart phone to a 4K monitor. Sway will automatically adjust the presentation elements to work with the graphics limits of the device.
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Second, unlike powerpoint, the presentation is not about embedding files, images other content all into a single file. The demo's I saw were heavy on using internet based content (copying from websites) using 'IFrame' links to the original source rather than making copies of the content, but you can also use content stored on the local device.
I did not see many text or formatting tools, but it does appear to provide enough for basic emphasis formatting.
I did not see ANY image formatting tools, because it appears to expect the images (videos) to already be in essentially finished form using other tools.
Yes, if you don't have an internet connection, it appears that Sway is hosed. I do not recall any mention of 'offline' viewing of sways. So, if offline viewing is a requirement, that appears to be a deal breaker.