Preview pdf-file if possible when doing `helm-do-grep` or `helm-do-ag`

Question

Suppose I do helm-do-grep or helm-do-ag on my tex-files, I can select a file on the results list and get a preview in another buffer by pressing tab. Is there a way (by pressing another key, not by redefining tab), to preview the corresponding pdf-file (if available) instead?

Another idea would be to define a variant of 'helm-follow-mode' say 'helm-tex-pdf-follow-mode' which previews the compiled pdf of the corresponding tex file if existend.

You may say that I could use pdfgrep, but with grep on the source files, I can for example find files containing specific comments (for example tags), not contained in the pdf-file or you can better search for math formulas.

Answer 1

Here is an example where you can use C-c C-c to bring up the pdf file in evince pdf viewer:

(defun my-custom-grep-cmd ()
  (interactive)
  (let* ((candidate      (helm-get-selection))
         (split          (helm-grep-split-line candidate))         
         (lineno         (string-to-number (nth 1 split)))
         (full-name      (substring-no-properties (car split)))
         (pdf-file       (concat (file-name-sans-extension full-name) ".pdf")))
    (start-process "viewpdf" nil "setsid" "/usr/bin/evince" pdf-file)))

(define-key helm-grep-map (kbd "C-c C-c") 'my-custom-grep-cmd)

I tested this on Ubuntu 16.04 using Emacs 25.1 and helm-do-grep-ag.