We pushed a fix that corrects the behavior of the Chart report item and now you can use the BitmapResolution Property
to define the resolution of the generated image in all formats inc. PDF. The fix is part of the internal build available in your accounts.
In the long term we consider the vector
rendering of the Chart item in PDF as a better solution and it will definitely improve the quality of the generated documents. The strongest point of the vector graphics is that they can produce images scalable to any size and detail. In contrast the raster graphics
(bitmaps) are resolution dependent and they cannot scale up to an arbitrary resolution without loss of apparent quality.
Thank you for the involvement.
All the best,
the Telerik team