If the signatures of the witnesses and names filled in on a kesuva fade is it still kosher?
What if it is to the point that one can’t read anything anymore?
Can this be corrected?
Their answer is that you should ask a rav with relevant experience to prepare a new ketuba. If there is a copy of your ketuba (e.g., in a central registry such as the one maintained in Israel by the central rabbinate), one can rely on it until one replaces the ketuba.
In their words
It is forbidden for a couple to be together without the husband’s basic ketuba obligation to the wife. [...]
There is a special document called a shtar ketuba d’irchasa that a couple can ask a rabbi to create when a ketuba is lost. It tells the story of the past obligation and the loss of the ketuba, and the new document replaces the lost one from the time of its issuance. This is done with the husband’s involvement. The gemara (Bava Batra 168b) and Shulchan Aruch (Choshen Mishpat 41:1) discuss a replacement document produced by beit din for one who possesses a document that has become (or is becoming) illegible. Even the witnesses themselves of the original document may not reissue an identical copy of the old one (Shulchan Aruch ibid.) because their authorization to produce a document ceased when they signed the first one (see S’ma ad loc. 5).
Resigning the document (which is parallel to rewriting other parts of the ketuba that faded) [...] is apparently not feasible. If the rewriting replaces something that is illegible, it is like writing a new document, which, as stated, cannot be done with the old date (a predated document is invalid – Shvi’it 10:5). Even if it is legible, it is still apparently a problem to write over it because people will be reading the new writing that covers the original (making it different from the discussion in Gittin 19a).