Unless someone figures out a hack, it's doubtful you can. I'm assuming the PS4 save system is similar to the PS3 save system, and they are encrypted.
When I looked into transferring console save files for the older Bethesda games, it was close to impossible for the PS3 (like with Oblivion, Fallout 3) whereas it was much easier for the 360 version (the 360 and PC versions of Bethesda games had compatible/similar save systems). I found some posts on another forum that it was possible for the PS3, but you had to send your save files to some guy who would do it for you (he had a hacked PS3 and some custom decryption software).
So, short answer is probably no, unless Bethesda creates a PS4-to-PC save transfer system. It might be in the realm of possibility since they are allowing mods to work with PS4 version of Fallout 4, but I wouldn't hold your breath.
If I were you, I'd just look to see if you can use the console in the PC version and cheat your way back to a similar point in the game, by giving yourself the skills, level and items, etc, that you had on the PS4. If the Fallout 4 console also has a complete quest command (like in Oblvion and Skyrim PC versions), you can also auto-complete the quests you've already done in your PS4 version. You'll have to find the quest ID number, too, and that's another command. Again, I don't know yet if Fallout 4 PC has the quest-related console commands, so you'll have to check.