Anyone? Pushing against a deadline here! Tnx..
I dunno for certain, but I'm pretty sure that you're coming up against screen resolution vs. print resolution. If you used very narrow strokes, then they're not being drawn onscreen at some zoom levels. The lines in your jpeg are some unknown number of pixels wide, so if the print res of your jpeg is high enough, then Acrobat is just not drawing them. You know, the fine lines in your jpeg are some number of pixels wide, and at print res you certainly can't draw all of those pixels onscreen. Heck, I wish one of the forum regulars who could actually explain this to you was in the room.
In terms of meeting your deadline... um... I am pretty sure that there is a preference in Acrobat to deal with drawing hairlines when viewing onscreen, but it's a local Acrobat preference, not something you can control in your user's view of the PDF. If it's only going to print, then don't worry about it, but if it is going to be downloaded and viewed onscreen, then I think I can dig up something for you.
What version of Acrobat are you using? Do you need to make a PDF that will display these lines on all versions of Acrobat on all kinds of monitors? Is the JPEG an image that you can edit, or is it some kind of photo? Can you post that JPEG online for us to look at?
This is a hard problem. It also depends on your screen resolution.
I would honestly experiment with lower resolution export and see if it helps. Remember screens top out around 120dpi.
Also, try bluring your image in Photoshop. In fact, try simulaing this behave your in Photoshop.
It doesn't sound like it is necessarily a JPEG or compression issue a all.
On the other hand you could also try Not Using JPEG.