If you review the attached screen shot of a PDF you will see that my Excel spreadsheet object prints very light. This is added to a Paper Space layer that is same layer as the Title Block, which is printing fine. The colorful solid objects are each in their own viewports.
I have set the OLE property "Plot Quality" to "Monochrome", also I have set the "Plot Style Table" to "monochrome.ctb".
To place the spreadsheet table I have Excel open, I select the columns/rows that I want and then Ctrl-C, I flip over to ACAD and Ctrl-V to place the object, I then resize it by dragging its handles. On screen, in ACAD, it looks fine.
I am creating the PDF using "Cute PDF Writer", which does an excellent job creating PDFs from many applications. I don't think it's related to my problem. I have tried ACAD's "DWG To PDF.pc3", but had a simialr problem, but worse in other aspects.
Rather than just simply pasting (PASTECLIP) your excel table into your drawing I would suggest using paste special (PASTESPEC) instead to insert your table as AutoCAD entities; that way you will be able to format the table as required in AutoCAD.
If you need to keep the table as an OLE object then you trying changing the OLESTARTUP system variable to control whether Excel is launched by AutoCAD at the time of plotting; this may give you a better result.
I tried PASTESPEC, but no change.
I determined that the problem was due to using the ACAD Proxy1 font. When I changed to other fonts the tables on my PDFs started coming out dark and now match what I see on screen.