Home / Putting Claude to work on real files
Working on a copy, never on the original
A file opened directly by Claude in a connected folder is modified in place, not on an invisible copy you would find afterwards.
When Claude processes a file located in a connected folder, it modifies that file itself, at the location where it sits. No backup copy is created behind the scenes: the document you reopen after the task is the same one as before, with the changes already written into it. This is what the previous lesson says about connected folders, applied to a single specific file.
Why making a copy is the reflex that protects you
The confirmation described for permanently deleting a file does not cover a change to its content. The difference lies in what each action leaves behind: a deletion makes a line disappear from the file list, it is visible; a rewrite leaves the file in place, with its name, its modification date up to date, and nothing on screen says the previous text no longer exists. Writing a new version over a file does not require the same explicit confirmation as a deletion, which makes a silent error more likely than a total loss: the file still exists, but its previous content has vanished without anyone seeing it go. A badly worded instruction, or an instruction hidden inside a document Claude reads along the way, can therefore rewrite a file you wanted to keep intact, with no alert stopping you along the way.
Duplicating a document before handing it to Claude solves this problem at the root. The copy carries the changes, the original remains identical to what it was, and you compare the two afterwards to decide what to keep.
The move in practice
The rule does not apply the same way everywhere. When the file is precisely meant to be updated, a draft you rework every week for example, opening it directly poses no problem since the change is the intended goal. Duplication becomes necessary as soon as the original must remain a reference, a signed contract, a version sent to a client, or any document whose exact original content you will one day have to prove.
Avant : Contrat_client_2026.docx
Après duplication : Contrat_client_2026_copie.docx (à traiter)
Contrat_client_2026.docx reste inchangéA copy name that is recognisable at a glance, with the word copy or today's date, avoids later confusing the two versions and mistakenly reworking the one that was meant to stay fixed.
Having the original processed or duplicating first
Contrat_client_2026.docx (modifié) Aucune version antérieure disponible
Contrat_client_2026.docx (inchangé) Contrat_client_2026_copie.docx (modifié)
On Monday, an accountant asks Claude to add a column to the cash flow tracking table stored in the connected Finance folder. Claude then announces that the column is in place. On Thursday, the same accountant wants to check how the rows were laid out before her Monday request, and reopens the table from the same folder.
Write in one sentence what this situation establishes, and in one sentence what it does not establish.
What this establishes: It establishes that Monday's work was carried out on the table at the very location where it sat, and that nothing in the process described set aside a copy of its earlier state.
What this does not establish: It does not establish what the accountant finds when she reopens the table on Thursday, since the situation stops before that, nor whether some mechanism outside the process described otherwise keeps a dated version of the file.
The three most common miscalibrations
- Too broad This situation shows that Claude destroys the data entrusted to it and that it must never be allowed to touch a working file.
- Too narrow This situation shows only that an accountant added a column to a table, which teaches nothing about working with Claude.
- Beside the point It establishes that the column added on Monday properly met the accountant's need.
- A file opened directly by Claude in a connected folder is rewritten at its own location, with no backup copy created automatically.
- The systematic confirmation exists for a permanent deletion, not for a modification that overwrites a file's previous content.
- Duplicating before processing keeps the original intact and lets you compare the two versions afterwards, rather than discovering a change after the fact.
- Prior duplication becomes necessary as soon as the file serves as a reference or as evidence, not for a document already meant to be updated regularly.
Duplicate a document before having it processed as soon as the original must remain intact, and name the copy so it is recognisable at a glance.
These points depend on an interface or a rule that may have changed since this was written. Check them on your own screen before relying on them.
- The exact means of duplicating a file before handing it to Claude, shortcut, context menu, or a function specific to Cowork, is not confirmed by the sources available and may differ depending on the storage platform used.
Every datable claim in this lesson links here to the public text behind it. A source that does not open proves nothing.
- Anthropic, using Claude Cowork safely consultée le 2026-09-02