"Based on the PostScript language, each PDF file encapsulates a complete description of a fixed-layout flat document, including the text, fonts, vector graphics, raster images and other information needed to display it." Source: https://en.wikipedia.org/wiki/PDF
HTML5 was not designed for typesetting and lacks such features. (For example, HTML does not specify page sizes.)
That is precisely my question! With increasing prevalence of documents being processed online, why hasn't it been the case that the HTML5 option appears as prevalent as the PDF option in say research articles? I guess a complete phase-out of PDF is not currently possible, but the provision of HTML5 alongside PDF should definitely be possible? I found some online options to convert Word documents to HTML5 too so it's clearly not technically impossible, is it?
It's also "fixed" - ie, probably as close to a WYSIWYG format as has ever been created (so far)
HTML5 is ice ... but it's not a 1-for-1 replacement/equivalent
Many research articles appear in printed journals. If a research publication uses online distribution rather than a printed journal, then perhaps HTML would make more sense.
Traditionally research papers have been distributed as printed magazines and volumes, so PDF has been a common interchange format.
>> I guess a complete phase-out of PDF is not currently possible, but the provision of HTML5 alongside PDF should definitely be possible?
Yes. It in most cases it should be possible, it depends on the use case, target audience, and perhaps the traditions surrounding what is being published.
>> I found some online options to convert Word documents to HTML5 too so it's clearly not technically impossible, is it?
Probably not. It depends on how the documents are originally written and the "expressiveness" of the documents needs. Many research articles are written using TeX or LaTeX (https://en.wikipedia.org/wiki/LaTeX) which, like PDF, was designed for typesetting.
Microsoft Word and most similar modern word processing software will export to both HTML and PDF. Most LaTeX-based systems also support HTML and PDF output. Other word processing and document preparation software may have a range of output and exporting options depending on what it was designed for.
It is more a question of what the target medium (web publishing, printing, ebook formats, etc.) is and what publishing format best fits the document's needs.
So I guess it's a matter of preference and medium too, although I felt that were an "HTML5 style" PDF possible, it would have been extremely useful in the fields I've published in. It's certainly better than filling up the page or the slide with a bunch of PNGs.