How to edit file information?

[pbvcity]

Hi. I met a problem.
First, I created a file named "A.afpub"
I then modified the content and save the file as "B.afpub"
Then I export the file as pdf, and save as B.pdf
At this time, I opened B.pdf and found that in its file information, title is still "A"

How can I modify this part of the file information, I can't find it anywhere.

[h_d]

Hi @pbvcity and welcome!

It's because the Title isn't necessarily the same as the file name.

In Affinity Publisher v2, pull down the Window menu and go to References - Fields:

 

Change the Title under Document Information. 

 

In Affinity Photo v2, it's Window > Metadata > then the File popup:

 

There doesn't seem to be any direct way to set the title in Designer 2, which frankly is a bit pants. (Forgive me if I'm wrong about this.)

However, if you have Photo 2 then you can switch into it from Designer (via File - Edit in Photo), set the title in Photo, then switch back to Designer (via File - Edit in Designer), export the pdf from Designer and its title will be the one you set in Photo. 

(All of these are from the macOS versions, but I would imagine Windows is identical in this respect.)