Friend, here are your two PDFs side by side, zoomed it to show how they will print to paper: they are identical, using the same Adobe Reader 9 PDF viewer.
Zoomed away, one is fain and the other is not as you note: this does not affect printing, just on-screen display. If I use a different PDF viewer, FOXIT Reader is my alternate, they appear as dark as each other.
Is your intent to print to paper, or only publish to PDF (there are no layers included so my guess it's not for editing or commenting)?
What are your DWG to PDF.PC3 file settings in the last tab's output options?
It may have to do with Autodesk plotting to Vectors and Adobe plotting to Raster. Sorry I don't have a better answer for you.
My intent is to email the pdf to our client, so the apparent gray really is an issue. It does look like JGerth's suggestion of first printing to DWF and then using the Adobe printer does fix the problem and only adds one extra step, which definitely beats a slew of saves. Just to throw it out there for anyone else having this problem, I also just found another solution similar to JGerth's by opening the faint pdf in Acrobat and 'printing to pdf' with the Adobe printer.
I attached a screenshot of my DWG To PDF PC3 setting, just in case there is something that raises a red flag. If there isn't anything that jumps out to anyone right away, I'm satisfied with JGerth's workaround as a solution.
Thank you everyone for the input-- I'll be printing this drawing set many more times in the future and this will ultimately save me a huge chunk of time.
In your settings screen, change Graphics > Merge Control to Merge instead of Overwrite. That seems to improve things. Merge is a good setting when plotting in black/grey only.
Merge does seem to help with the faint lines, but then it produces a strange pixelation in regions where a fill or mask is used (see attached).
Too bad, I think creating a good PDF is a bit of an art form Maybe try a professional PDF product. I've heard really good things about Bluebeam (Bluebeam Revu CAD) Apparently they are very good at resolving issues.
Merge is probably similar to Gradient Hatches and not implemented well. Gradient Hatches rely on DirectX and you end up with lo-res raster graphics. So that is an AutoCAD issue as opposed to printer driver.
Install Ubuntu preferably on another computer. Print onto a flash card all your pdfs using acad 'Dwg to pdf'. Transfer flash to Ubuntu computer and using ubuntu document viewer print or email pdfs without any feint lines. Works every time.