Thanks couet for your modifications, that’s great news. I will be now able to export my TH2 to pdf instead of png 
Concerning delaossa, I think that what one should ask for is to have the possibility of filled 1D or 2D transparent histograms also in the pdf output, rather than profiting from an anti-aliasing bug for mimicking transparency. There is this post:
[Transparent histogram fill style
But it seems that the exported pdf does not contain the transparency for solid areas, and the densely dotted fill style mimicks it but is ugly for pdf. In my case, I use full solid areas, that are not transparent in the exported pdf, and then edit by hand the pdf with inkscape and add the transparency to these fill areas (now fill areas and strokes ). Then I export back to pdf and it renders perfectly.
If inkscape can do it, then ROOT may also be able to include this in the future. But I think we need to create another post for this “new” request 