Fallout 4’s location is straightforward, but modded restoration is not. A base .fos file can reference content from plugins, and F4SE can add a paired cosave. The safest archive therefore includes the full save directory plus enough information to rebuild the mod environment. A failed load after moving PCs is not automatically evidence of file corruption; missing plugins, changed load order, or an absent cosave can be the real cause.
Identify the exact save you intend to edit
The researched Fallout 4 PC save location is Windows: %USERPROFILE%DocumentsMy GamesFallout4Saves | Linux / Steam Play: Steam Play: <SteamLibrary-folder>/steamapps/compatdata/377160/pfx/. Known file/folder pattern: *.fos
*.f4se (when created by F4SE). Storefront context: Steam, Microsoft Store / Xbox app. The standard Documents path is the primary Windows reference. Microsoft Store packaging can differ, so locate the active edition before restoring a file. Do not edit a similarly named file from a different profile, edition, or cloud cache.
Make an untouched backup first
Copy the complete Saves directory. On F4SE setups, keep matching .fos and .f4se files together and record the installed mod/load-order state. Keep that copy outside the live save directory and do not overwrite it with later experiments. Cloud context: Cloud behavior depends on storefront. OneDrive may also synchronize the Documents tree if Windows folder backup is enabled. If a launcher can synchronize the save, prevent it from silently replacing either the original or edited copy while testing.
Understand the format boundary
Base Fallout 4 saves use .fos. F4SE-enabled installations can create companion .f4se cosaves; preserving only one side of a modded save may remove script-extender state. File-extension context: .fos, .f4se Compatibility note: A clean base-game save and a heavily modded save have very different restoration requirements even if both use .fos. These facts help identify the save but do not automatically reveal every field, checksum, encryption rule, or version-specific structure inside it.
Use only a Tool whose claim matches the file
Generic viewers and diff tools can inspect bytes without claiming game-specific semantics. A game-specific editor should be used only when its Tool page explicitly lists Fallout 4, a matching supported version/container, and a Verified operational runtime. A planned URL or Game Hub is not evidence that an editor exists.
Test the edited copy safely
Write to a new output file when the Tool supports it, keep the original backup, restore the edited copy into the correct profile/storefront location, and launch the game only after the file operation finishes. If the game rejects it, If an apparently valid save crashes on load after migration, verify missing plugins and script-extender dependencies before replacing more files. Also check whether Documents is redirected by OneDrive. Return to the untouched backup before trying another change.
Verification context: The standard Windows and Steam Play save locations were reviewed against current PCGamingWiki coverage. Format notes distinguish base .fos saves from optional F4SE cosaves.