Fix page view overhead of pdf file among automatic reports

[choonghyunryu]

In the case of a scatter plot or Q-Q plot among the plots included in the report,
When the number of data is large, it may take a lot of time to switch pages.

This is because the plot attached to the document is a pdf file, not a bitmap file. When reading the plot included in the pdf file, the information corresponding to the number of observations is read and rendered on the screen.

So, plots of data with many observations should be attached as bitmap-based image files.