Shortcut to open file with alternative application You can set certain applications to open certain files by default. For example, .pdf with Preview, .jpg and .png with Preview, and .txt files with TextEdit. However, sometimes you want to open them with alternative applications – .pdf with Skim, .jpg and .png with Photoshop, and .txt with Chocolate.

Is there any way to open a file you have selected in the Finder in its respective "alternative application" with a specific keyboard shortcut, for example F1? 

It is possible to open files in specific application using a keyboard shortcut with AppleScript via Automator, but I am not aware of a way to open the file in an application depending on the type of file it is.
I don't think there is a way to associate an alternative app for every extension so there might be no way to do it via script unless you want to write your own app.

Why not use 'Open With' from context menu? I use it all the time, pretty much as fast as pressing hot key shortcut.