Optimization for exporting CAD drawings to PDF files

[tmac971031-eng]

1.Thank you very much for the optimization of the previous CAD version conversion issue.
2.Currently, all contents are exported onto a single page when exporting CAD drawings to PDF. For engineering drawings, multiple drawing borders are often placed in Model Space. It is expected that this function can identify each drawing border/rectangular frame and export it as an individual PDF page.

[KnifeLemon]

Thanks! This is the same as #535, which tracks finding the title-block frames in model space and making a PDF page per frame. Please follow #535 for updates.