Adding bleed margins before sending to a print shop

I need to add a bleed amount (extra margin to be trimmed) of 2mm before sending the final pdf to a print shop. I use a format next to the “concert” format, in my case 23 x 30,5 cm.
Any advice how to achieve this? I cannot find anything in the manual.
Thanks to everyone who can help.

Edit: I could increase the “Page size” in the Page Layout to 23,4 x 30,9 cm, but then the whole page layout increases, too, which is not what I want, of course. I could decrease the “Space size”, but this workaround seems a bit cryptic to me …

Bleed is only necessary if you have graphical elements that go right to the edge the page, like a tint panel or a photo.
Dorico does let you print to a printer using a larger sheet size than the page, and there’s an option to add crop marks; but you can’t draw objects outside the page area, so even if you did have a graphic up to the trim, you couldn’t bleed it over the edge, anyway.

Assuming you have white margins round the edge of the page, then the print shop should be perfectly capable of dealing with a trimmed page.

You could increase the page size in Layout Options and correspondingly decrease the page margins?

@Lillie_Harris , wouldn’t you need to check all the frames’ constraints for that first? In my experience, changing the page size makes everything go screwy unless I’ve nailed those down.

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Probably, yes.

Thank you, @benwiggy and @Lillie_Harris
A print shop always needs to adjust bleed margins, regardless of wether there are objects that go right to the edge or not. So, therefore it is necessary to adjust bleed margins.
@benwiggy: yes, you can use other printers / other page sizes and then set crop marks … but in this case I would be forced to use a DIN A3-printer.
I’m going to send my pdf to a big Berlin print shop and they don’t need crop marks, they just need the correct page size with added bleed margins.

EDIT: They told me at the print shop that I should send the pdf without the bleed margins, they would add them by themselves … but I think there should be a way to add bleed margins within Dorico (like in professional graphic design apps like InDesign).

Any decent printer will have pre-press software to add the marks and margins that they need. – Ah, just seen your edit confirming as much.

If you really must, then you’ll have to import the trimmed PDF into DTP software, like Affinity Publisher, and then output a new PDF according to the spec.

I’m not sure that any notation software caters for bleed. Finale doesn’t (as far as I can tell).

Yes, this could be another solution. However, I hope there will be a way within Dorico in the future. Thanks for spending your time and giving advice.