Incidentally, I wonder if you can answer a question: I want my books in an electronic format, that will be usable for the rest of my life or longer, and which preservers annotations.
As far as I know, PDF/A is the only format that fits the first two specs. I know annotations are in the PDF specs but is it reasonable to think that annotations I make today will be readable - and updatable - in (e.g.,) 30 years?
Yes, that is quite reasonable. The simple text annotations are quite easy to work with when using a PDF library and the standard tries to be backwards compatible where sensible.
The PDF 2.0 standard removed some parts of PDF 1.7, like the proprietary XFA forms. But most things stayed in PDF 2.0 and one can expect that those annotations will also be available in future iterations of the PDF specification.
And generally, since future PDF viewers will need to be able to view older documents (think: all the (signed) documents created by governments), you can expect PDFs created today to be usable in 30 years and more.
As far as I know, PDF/A is the only format that fits the first two specs. I know annotations are in the PDF specs but is it reasonable to think that annotations I make today will be readable - and updatable - in (e.g.,) 30 years?