One errand, several uses
People order a Bulgarian translation for one purpose and then meet it again. A record that opens a bank account is the same record a school, a landlord or an employer later asks about. Bulgaria accepts a translation certified in this way, so the set you hold now will normally do the next job too. That is why the copy is worth filing rather than folding into a coat pocket.
The signed set and the scan do different jobs
Treat them as two tools. The signed pages carry a real ink signature and a date, and they are what you take to a counter that wants paper in hand. The scan is for uploads, for email attachments and for your own reference. An official Bulgarian translation in Plymouth is usually delivered as both, and mixing the two up is the most common reason someone turns up with the wrong thing.
When the source record changes, start again there
A translation cannot update itself. Where the paper is a civil record and the entry has been corrected or reissued, Plymouth Register Office at Derriford Park, Derriford Business Park, Plymouth PL6 5QZ issues a certified copy showing the record as it now stands. The Bulgarian text is then written from that copy. Translating an old version first and patching it afterwards costs more than doing it once in the right order.
Per-page cost and turnaround
Cost is £25 for each page of the record, which makes a long file predictable rather than surprising: count the pages and multiply. The wait is 2–4 business days from a clean scan, dropping to 24–48 hours if you take the express route. Ordering a second signed set later runs on the same clock, so a duplicate is not a slow favour but simply another short job.