(I use this feature every day, multiple times a day, to export vector line art to PDF files - and have NEVER had this issue until now).
All vector lines are being transformed into bitmap rendered line segments (they are several pixels wide and have gradations in shading within the width and length of the lines). No options available under 'Publish to PDF/Settings' dialog box to remedy this issue. Tried every option under the 'PDF Preset' dropdown (Archiving, prepress, document distribution, etc), but that did not fix the issue. The dialog box also shows "1 Issue detected in document', this issue is 'there are fonts below 18pt in your document'. I don't know why that would affect the vector lines, but it's worth noting as I did not have this issue before the update.
Work-around: The only work-around I have found is to use the 'Print' command, then change printer to 'Adobe PDF'. This results in vector lines remaining in the final pdf, not being converted into bitmap. This is, however, not the same as Publish to PDF, and takes significantly longer to 'Print' the file (ie, it's not an ideal workaround).
Firstly, Thanks to Ronny Axelsson for identifying that the pdf files imported from autocad had transparencies integrated into them (though they weren't really visible until you publish), and once disabled the vector lines would publish correctly. The second part to this issue was why the Autocad output pdf files (as of 9/9/24) were adding transparencies (when 'plot transparency' was toggled off in the plot dialog box). The solution (found in a 2018 post on Autocad forum) is as follows:
In the Plot dialog box:- Properties(next to plotter name)- Device and Document Settings- Graphics- Merge Control <Lines Overwrite>
Set to "Lines Overwrite".
Ours was set "Lines Merge" which caused this problem. We don't know how or why this setting changed. Most likely a user here changed it without realizing their error. If changes are made in the 'PDF Options' dialog box, it prompts you to save over the master file for that print option. Once changed to "Lines Overwrite", the imported pdf files will publish from Corel as vector.
Thank you KRLightning.I'm glad I could help and also very glad to hear you found the cause to why the objects had a transparency.As Bobby mentioned, transparencies can be very unpredictable when exporting and some features in Draw's transparencies may not have an equivalent in the PDF file format, so all they can do is to convert to a bitmap, which of course isn't ideal.