Add link to the pdf version of the documentation to the html pages, fix

#28604. (#30449)

(cherry picked from commit 21f7a1e)

doc/src/index.md

@@ -20,6 +20,18 @@ Markdown.parse(String(take!(io)))
 ```
 Please read the [release notes](NEWS.md) to see what has changed since the last release.
 
+```@eval
+release = isempty(VERSION.prerelease)
+file = release ? "julia-$(VERSION).pdf" :
+       "julia-$(VERSION.major).$(VERSION.minor).$(VERSION.patch)-$(first(VERSION.prerelease)).pdf"
+url = "https://raw.githubusercontent.com/JuliaLang/docs.julialang.org/assets/$(file)"
+import Markdown
+Markdown.parse("""
+!!! note
+    The documentation is also available in PDF format: [$file]($url).
+""")
+```
+
 ### [Introduction](@id man-introduction)
 
 Scientific computing has traditionally required the highest performance, yet domain experts have