Photoshop elements 2020

Made a chart in autocad lt 2022.  Converted to a pdf file format.  Trying to change to a jpeg to insert into a photobook.  I have done this before without any problems.  I opened the file in photoshop editor and this is what it looks like.  When I go to save as in jpeg format I can see it lightly behind the checkerboard (which I dont know why it looks like that so I attached 3 screen shot.  After I save as (jpeg) and open it up its very light.  Why is that .  Thank you