Whereas the precise legality if this depends on the rules/laws of the body receiving the documents and what they are about, there are some generally applicable considerations as follows.
The whole idea and common practice of accepting digital scans of paper documents for legal purposes without seeing/receiving the papers themselves is very susceptible to legal challenges based on the allegations of forgery. At the same time, everyone loves and appreciates the convenience of not having to handle actual papers, and therefore is prepared to some level of leniency by not being too pedantic and meticulous in following paper handling procedures originating from pre-digital eras: after all, those procedures do not quite fit in the present digital-centric world.
So, the extent to which anyone cares that signatures were digitally copied/pasted and not physically put with a pen depends on the risk, stakes and liability involved. Say if you are "signing" and emailing "scans" of a rental agreement to a real estate agency, you will unlikely be questioned or ever asked to provide the paper originals. But if you are buying/selling real property, not only will you be asked to actually sign papers, but do it in the presence of a lawyer who will witness your signature (unless the whole transaction is done using truly digital (cryptographic) signatures).
Similar approach is taken even by the courts of law. For example, in New Zealand, whilst all documents filed with the courts need to bear signature on them, the actual approach to handling this depends on what the documents are:
- Documents that initiate court proceedings (e.g. Statement of Claim) and affidavits need to be physically signed and delivered to the court
- Secondary documents, even though "signed" (such as memoranda, submissions, certain applications) can exist in computers only and, in practice, do not ever need to be physically printed/signed. The courts will accept them by email and not ask the originals.