I have been generating PDF files from Alibre Design (MCAD) since 2005 with no problem. I 'print' the pages with the current Adobe Acrobat Pro and then place them in the pages of my magazine layout in InDesign.
Recently, when I place a PDF generated from Acrobat Pro, PDF Creator and one or two other PDF generating packages and place the PDF in InDesign, I find random and fairly thin files in most of the placed pages. But not all.
So far the lines have not appeared in the PDF files generated by the Export function in InDesign.
What I am worried about is the possibility of the lines showing up in the PDF generated by the Export function. That would force me to use Acrobat to generate TIFF files from the PDF files. A significant time sink if necessary.