Adobe Acrobat Pro XI on MS Windows, as well as Adobe reader on Windows, also refused to open the files.
I suspect this may ultimately be a poppler bug; both evince and okular use poppler. In particular, there's a bug that poppler can't handle XFA, and I'm pretty sure that OpenTax uses XFA. OTOH, OpenTax uses pdftk to fill in the forms. My work-around was to open the pdf's in evince and then print to pdf. Oddly, the resulting files were much shorter than the originals; they also seemed to be better formed. Acrobat Pro was able to put them together. I haven't tried any of the Linux tools on the resulting files. Ross
