What Adobe PDF setting for readability of not-Black-on-White and very Fine Text within Picture ?

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What setting for readability of not-Black-on-White and very Fine Text within Picture ?

I need help to detemine Adobe PDF setting for readability of Text within Financial Report on A4 Portrait paper.

Text Readability becomes more important (than other factor such as true-to-original color) when the Text has the following characteristics

1. fine (Arial Size 6)
2. Not Black on White.
3. within Picture such as Chart

How to maximize Text readability within Picture?