Acrobat reports, accurately as far as I know, the actual font type used in a PDF. These types don't exactly correspond to the font file types in use, and include Type 1, TrueType, CIDFont, and OpenType. However, converting between these font types is entirely possible, and a lot of PDF generators will do this, for reasons of compatibility, efficiency, or just because they've always done it that way. OpenType was not in the original PDF design, so asking for an old PDF version will mean you don't get OpenType font format, but a conversion. Some software doesn't bother to export OpenType at all.
When creating PDF files, with a few limited exceptions, when faced with OpenType fonts, either those OpenType CFF fonts with Type 1 Bezier curve outlines and hinting or OpenType TrueType fonts with TrueType outlines quadratic curves and hinting, Adobe applications will extract the equivalent Type 1 or TrueType font and embed them as either Type 1 or Type 42 (TrueType) fonts in the resulting PDF files.
The only general exception is when creating forms, in which case if the font used for filling out the form is in any OpenType format, the full OpenType font will be embedded. The reasons for that are (a) all the glyphs of the font might potentially be needed and (2) the full OpenType font has metrics that are useful or necessary for proper layout of input data.
Conversely, fully embedding an OpenType font bloats the PDF file with more data than is necessary for fully and properly rendering the text in the PDF file.
Note that in the OfficinaSans, if both the original Type 1 and the subsequent OpenType CFF font were sourced from Adobe, you would see a difference in the PDF file. The OpenType version of the font would be named OfficinaSans Std although embedded as a Type 1 font.
Hopefully that gives you insight into what is actually going on.
When I asked the original question, I was suffering from a senile delusion: In my mind, I was recalling seeing OPENTYPE fonts listed in the Fonts tab of Acrobat's Document Properties. That is what I was trying to achieve with this new project. But I've now looked back at dozens of PDFs I've created and NONE of the fonts listed in that Fonts list appear as OpenType ... they either appear as Type 1 or TrueType (as you described). I don't know where that delusion came from.
I'm sure this follow-up question will prove I still don't "get" it: When I went through the process of replacing the missing Type 1 fonts with their OpenType equivalents ... was I completely wasting time? Did making that change improve anything, in any way?
One thing I did notice: What I got from my customer was a PACKAGED InDesign file, accompanied by a Fonts folder that contained all those PFB and PFM files. But when I PACKAGE this InDesign file I've just updated, the Fonts folder that's generated contains the OTF files.
I have not yet had my "aha moment" with this... derp. I think I slept through OpenType 101.......
Actually, you asked two questions.
The first is that of the value of OpenType CFF over Type 1. This is fairly simple. OpenType fonts allow for Unicode mapping and the ability to have a very large number of glyphs in a font. With Type 1 fonts, for a particular family and style, if you wanted Small Caps, non-Latin alphabets, old style figures, ornaments, etc., you had to have multiple fonts and keep track of how you keyed those special characters. With OpenType, all the glyphs can go into one font with a distinct coding for each glyph. OpenType also facilitates programs such as InDesign and Illustrator (and even to some degree recent versions of Microsoft Office) to automatically access ligatures, swash characters, small caps, lower case / old style figures, style sets, etc.
The second question you pose is related to a packaged InDesign document. For Adobe's fonts, the scenario you pose should not ever happen. Why? We purposely changed the name of the OpenType versions of the fonts such that there would be no confusion as to which format fonts were being used. For example, “Helvetica” as a Type 1 font became “Helvetica Std” as an OpenType font. “Adobe Caslon” as a Type 1 font became “Adobe Caslon Pro” as an OpenType font. (Std fonts have “standard” character sets with ranges of glyphs covering Western Latin character sets and basic numbers and symbols. Pro fonts typically have much more extensive character sets including extended ligatures, alternates, small caps, swash characters, support for non-Western Latin glyphs, etc.) Thus, for Adobe fonts, if you make the switch from Type 1 to OpenType, you must change the font selection in your styles (preferably you do use styles) or otherwise do a search and replace for font names. Another reason why we changed the names and forced the explicit user update is that although we tried to maintain compatibility between Type 1 and OpenType in terms of font metrics (especially advance widths for each glyph), we were concerned that any slight difference might lead to some unexpected page relayout. Thus, when changing from Type 1 to OpenType, one should check that no undesirable changes have occurred, and if they have, make appropriate adjustments. If you changed from Type 1 to OpenType simply by changing the fonts installed on your system and they had the same names, you were clearly not using fonts in the Adobe font library.