Hello,

I came upon this screenshot on a very old page on Microsoft's website. https://www.microsoft.com/typography/links/News.aspx?NID=1135. I am curious about the font in use. I compared it to Corbel and Segoe so far which I thought might be the font. Also, lowercase "e" and "a" look slightly different between the bottom left screenshot with bigger font size and the rest of the remaining three.

Can you see which font it may be? Thank you!

Frutiger  Suggested by jerseygirl 

The list of fonts I have for MS Reader from several years back are

Linotype Frutiger
Berling Antiqua
Lucida Sans Typewriter

I'd go with Frutiger on this one, for all four screen shots.

(Unfortunately, I can find no source to verify that font list.)

Thank you jerseygirl.

It looks very similar to Frutiger indeed. I thought that it must be one of the old screen-optimized Windows or Office fonts but didn't look like any of them.

Reader came with its own fonts. I remember installing it just to see which fonts it would install. There was also a dingbat font (Bookdings).
I uninstalled the Reader software but kept the fonts

Don't know if the software was capable of using fonts besides the ones that came with it. Maybe, but MS Reader wasn't known for its flexibility.