I get the address from the database and I want to load the pdf that is in that address but this error appears Response.Redirect ("C: \ file.pdf");
The pdf file (s) need to be in the directories of your web application. It can be in the main directory of your app, or in a specific folder for pdf files (I recommend this second option).
If they are files that are fixed, and they are already in your Visual Studio project / solution, do not forget to mark them as content files and be copied either 'always' or 'if they are new'.