Problem with line and text rendering in PDF

Hello, I'm having a small rendering problem when editing PDFs.

I am made to draw plans  via a macro in Excel using original DWGs.

But from some of these original DWGs, the cartridge, which is a priori identical in every way, ends up with a slightly altered PDF rendering (blurred line and half-erased letters ). And I don't have that in the other DWGs.

The cartridge is made from a block contained in each of the original DWGs, but no matter how hard I try to edit these blocks, I can't find any differences in "Properties"  that could explain the phenomenon. The blocks are also edited in the same layer in the final DWGs. I don't see anything else that could modify this rendering!?

Do you have an idea?

Thank you. Regards.