Actually, "reflow" is a feature of Tagged PDF.
Distiller's PDF/A-1b job options do not deal with providing a tagged output PDF.
To do this you'd configure Acrobat PDFMaker.
Under the Settings tab tick "Enable Accessibility and Reflow with tagged Adobe PDF".
Under the Word tab tick "Enable advanced tagging".
Provided the authoring file was mastered so as to support a proper logical hierarchy of content Acrobat's PDFMaker provides tag management for the output PDF such that the structure tree is at or close to where it must be.
With the tagged PDF in hand use Acrobat Pro to perform the requisite post-processing to assure a well-formed structure tree (working out of the Tags panel).
Thanks CtDave, that makes sense. So to get reflow, I would need to specify it directly via Acrobat's PDFMaker. Word 2007's Save As PDF/A 1-b by itself will not by itself ensure reflowable text. Got it.
Just a "heads up".
For those who need to or desire to provide accessible PDF the pending release of the following documents will be "must have" references.
--| The ISO Standard for PDF/UA (ISO 14289-1
--| PDF/UA-1 Technical Implementation Guide
--| PDF/UA-1 Technical Implementation Guide: 32000-1
(ISO 32000-1 is the current ISO Standard for PDF)
--| Achieving WCAG 2.0 with PDF/UA
(WCAG 2.0 for PDF is PDF/UA)
The latter three documents are expected to be available on AIIM's web site.