If there is no direct way for the crawler to reach the page, it won't be indexed + if the page is so hard to reach, it probably wouldn't pass much authority onto your site.

I'd still get the link if it's on a good website for potential referral traffic but wouldn't worry about trying to get it indexed.

We need more info. Site? URL the 404 had an inbound link from?

While going through your site, the crawler encountered a link that it followed which resulted in the server returning a 404 status code (not found).

1. If you want to deindex all PDF files, I recommend using the x-robots-tag in .htaccess - https://yoast.com/x-robots-tag-play/

2. If the PDFs are pdf versions of existing pages, I would set canonicals to point to the URL you do want indexed (#2 on http://moz.com/blog/htaccess-file-snippets-for-seos )

use #2 if search engines can see the content that would be on the other pages. if they can't see it, then use rel=next/prev

Cool cool. No breadcrumb code but it still shows up. My guess is that it assumes the » implies a breadcrumb. Try changing that to something else... | or > ... and see if it goes away.

In TheaterMania's case, each tab is a link to another page, not hidden divs.

Both is the way to go. Silos are essentially structuring your pages so that per topic, there is 1 master article and multiple supporting articles that link back to the master article. The topic only links to pages relevant to the topic and not other sections of the site.

You can use breadcrumbs in conjunction with a silo as the structure is suitable for them.