I would like to ask if anybody knows of a possibility to render pdf file inside emacs. I noticed with w3m browsing a web page with a link to pdf it actually open with doc view it in another buffer (as you can see). How can I do it with other packages ?

As long as you have Ghostscript installed, you can view PDF files in Emacs just by opening them as any other file, with C-x C-f.
doc-view-modeshould start automatically, but if it doesn't, you can do it manually with M-xdoc-view-mode. More information is available in the manual.