How proof of a signature travels
A foreign office cannot know a British signature on sight, so it needs someone it trusts to vouch for it. Treaty members accept a single slip from each other. Everyone else asks their own consular officer to look at the file. Guinea belongs to the second group, which is why this job has two stages instead of one.
Guinea and the Hague Convention
Guinea has not joined the Hague Apostille Convention. A British paper bound for Conakry, Kankan or Nzérékoré requires embassy legalisation on top of whatever the Legalisation Office has added. The United Kingdom signed the treaty decades ago, so the stamp is issued here without difficulty, but issuing it and having it honoured abroad are different questions.
The Sheffield end of the work
Nothing in the British stage is local. One office covers the whole country by post, so there is no legalisation desk in Sheffield to visit. The city's contribution is the source paper: the Register Office at the Town Hall for civil records, a university for a degree, an employer or solicitor for a signed business document.
An apostille from United Kingdom to Guinea is easier to manage as one batch. Gather every paper the job needs, send them in a single round, and keep spare certified copies at home. A mining contract that starts on a fixed date leaves no room for a second attempt at the consular stage.
French, and the papers the mines ask for
French is the language of government there, so a stamped English document usually travels with a French version beside it. Prepare those words after the final mark. A translation made early describes the paper before its stamps, and the receiving desk is looking at the whole bundle rather than the sheet you started with.
What leaves Sheffield reflects the work waiting at the other end. Bauxite, iron and construction projects want engineering degrees, chartered memberships and safety certificates, each proved before a work permit moves. Health and aid postings send police records and medical registrations. Personal records make the same trip, quietly, behind a marriage or a family claim.