Cannot find or create the font 'tahoma'

Tahoma is a Windows font, means it is distributed with Windows OS not with Adobe applications.
Check the Windows font folder. If it is not present there, the font was not installed with your current OS.

Tahoma is installed in the fonts folder. What I am doing is opening an AutoCAD .dwg file in AutoCAD sent to me from a customer and using the export tool to export as PDF so people I work with that don't have AutoCAD installed on their computer can view the drawing. The only thing that appears with the dot dot dots in the PDF is a dimension that has the degree symbol. Think the degree symbol is what is causing the problem?

Sounds like AutoCAD doesn't embed the font correctly into the PDF.
What if you use another font such as Courier? Does the same error appear in Reader?

That's the problem, this drawing file came from a customer and I can only open the AutoCAD file as "read-only"...

Do you have Acrobat?
Then you can use the Preflight-Plug-In to fix the faulty PDF.
If not, you have to talk to the author of the dwg-file to fix this in AutoCAD or what else app he's using.

I downloaded the Adobe Reader X, and that's what I am using. I'm not sure what you mean by do I have Acrobat?

I mean Adobe Acrobat the app to create and edit PDF files.
Reader X is only for viewing PDF's and cannot apply changes.
For those tasks you need Acrobat.
You can download a trial from Adobe's website.