In ArtPro+, you can place PDF files, e.g. for step & repeat purposes.
The PDF in which you are placing the files can only be a PDF+ file. You can not place a PDF if the current document is a Normalized PDF file.
The PDFs that you are placing can be a mix of PDF(+) and Normalized PDF files.
As of ArtPro+ 18.1, you can also convert Normalized PDF files to PDF+. (See User Guide, "Convert to PDF+" chapter).
It is important to understand that both file formats (PDF+ and Normalized PDFs) have properties that the other format does not support.
For more information on the differences between PDF+ and Normalized PDF, please read the "PDF, PDF+ and Normalized PDF" chapter in the ArtPro+ User Guide.
When placing or converting Normalized PDF, you may want to apply some rules to facilitate the conversion, so less manual corrective action is still required afterwards. See Preferences > Normalized PDF tab.
At this point in time, the only real difference between activating the Normalized PDF conversion rules in the Preferences or not, lies in the way technical inks are processed.
Technical inks are supported in Normalized PDF but not in PDF+.
PDF+ does have the concept of Processing Step Layers, which serve the same purpose as technical inks: allowing to visualize objects that are added to the file for technical reasons but that do not belong to the final artwork.
If you apply the conversion rules, you can map specific technical inks to specific Processing Step Layers. You can customize the rules: you can add, remove and reorder rules. They are case insensitive and are executed from top to bottom.
If you choose not to apply the conversion rules, technical inks will just become opaque inks in the resulting PDF+ file. You can still manually move such an opaque ink to a Processing Step Layer after placing or converting the Normalized PDF file, but the advantage of applying the rules upfront is that all conditions for colorants in the Processing Step Layer* are met automatically. (*Conditions as determined by ISO 19593-1).