The first question that needs to be asked is whether this happens if you add the text in the same font using a more suitable tool such as InDesign. Use of Photoshop for a "major publication" is likely to get less sympathy than we might hope for.
That makes sense. I should use InDesign, perhaps, and plan to play around with it more. However, I find it less intuitive for drawing and design work. Maybe that's just me. This isn't a print publication, but rather a web publication. I am not new to art or design, but am rather new to digital design, so I have been working with the tools that are easiest for me to manipulate.
However, I did find a workaround. Someone in another forum mentioned that it was an error generated by designing with the Transparency option, which I need when overlaying multiple images, logos, etc. Photoshop and Acrobat just don't play nice together in this way, it seems. So I exported the document as a PNG with Transparency UNselected. Then I saved the PNG as a PDF from there and, voila, no more random bolding of text.
Thanks for your response.
I certainly wouldn't use InDesign for drawing or fancy design work. The key is that people mix their tools. Typically for print publication it's Photoshop (photos/scans/raster effects), Illustrator (drawing/text effects), InDesign (assembly, text). The boundaries keep moving, as Adobe keep adding features to each product, to the extent that the work can often now be completed in one tool - but not necessarily for the best results.
If your end result is a PNG, I would consider staying in Photoshop where you have absolute pixel control. Consider making blocks of text in InDesign and importing. But if your end result is a PDF I'd definitely stay in InDesign. Transparency in Photoshop involving text is messy, as it will have to be rasterised/vectorised there so far as I know.