How do I upload PDFs/Excel files for viewing by the forum?

There isn't a way to upload a PDF or Excel file (visibly) here at a2k. The forum can only support JPG, GIF, or similiar image format. You are going to have to use a document hosting site Dropbox or Citrix Sharefile or create a blog with Squarespace and upload the document there.

And share the file url link here. Keep in mind that you are new and your provided links will be looked upon with skepticism. People will think they are possible spam or phishing links.

Another thing you can do is take a screen shot of your Excel file and at least the image can be shown, and it can be hosted at Image Shack or Photobucket.