Bad resolution on pdf overlay

Hi there
When preparing an pdf overlay the pdf has not a high resolution. These makes it very hard to place the red and blue marker correctly. The original pdf is very sharp with high resolution.
It is a new issue. In the last years I never had these problem. On the left side of the attachement you can see the pdf in the pix4d window and on the right side the original pdf.
Any suggestions on how to display the pdf in a good resolution so that I can place the markers a the right location