We are using Microsoft Information Protection SDK File API 1.14 (Microsoft.InformationProtection.File) with .NET6 in order to assign sensitivity label on files. When we try to do it on a PDF file that was previously assigned with no problem, we get "The file is protected by signature" error from the FileHandler. The file was previously assigned so we see all the MSIP label custom properties in the file. This issue happen for specific file, however, we don't understand why is it refusing to assign the label on this file that was already assigned in the past.
- We tried using an older copy of the file (without the MSIP properties) and we got the same error.
- We modified the file using Word (the application remove some of the features in the file like eSign), and it did assign the label on the new file without any problem.
- We tried running the assign action with SDK 1.13 and also 1.12 - we got the same error.