What other applications call "outlines" or "bookmarks" is called "Content" in Okular. it is shown on the left panel as a table of content, also giving links to the actual pages.

I haven't found Okular allows adds or editing some lines and links to the "Content" yet. Do I miss it? Thanks.

Okular supports bookmarks:
http://docs.kde.org/stable/en/kdegraphi ... ement.html

The table of content of the document is something part of the document which can't be changed.

i was not talking about editing "bookmarks" but "Contents". See the part singled out by a red box below
Yes, "Contents" are part of the pdf file, and I want to add and edit some lines in the "Contents". How can I? Thanks.

tosky wrote:Okular supports bookmarks:
http://docs.kde.org/stable/en/kdegraphi ... ement.html

The table of content of the document is something part of the document which can't be changed.

timlee wrote:i was not talking about editing "bookmarks" but "Contents". See the part singled out by a red box below
Yes, "Contents" are part of the pdf file, and I want to add and edit some lines in the "Contents". How can I? Thanks.

It's not possible to change the content; the possibility for changing it would means introducing editing features in Okular.

I realise this is an old discussion, but I thought I would add my comment here as I googled for the same issue and the discussion came up as one of the first hits.
It appears bookmarks, or "Contents" as Ocular terms it, can still not be added or edited in Ocular.
Further searching revealed Master PDF (https://code-industry.net/free-pdf-editor/) as the solution. It does it almost as well as Acrobat Professional, which I used when still living in Windows-land.

Bookmarks (which can be modified) are not the same as the hardcoded table of contents.

Agreed, that is the way Okular defines bookmarks. Other packages use the term differently.
Okular stores an index to the locations you store as bookmarks in a different location, as per the OP.
Adobe and Master uses the term "bookmarks" for Okular's "contents". Both these packages allow you to store this index within the file and edit it, making it available for use in other applications, or if you move or share the file.
I just had the experience of creating bookmarks in Okular this morning and then changed the directory name, breaking the bookmarks. Editing the the file path in the bookmark does not update the bookmark, rendering the whole index useless. I had to change the directory name back to use the (bookmark) index again.

Sure, but this discussion was not about the bookmarks, but the table of content defined inside a PDF.

Yes. But I argue that Ocular is at fault here for using the term "contents" where everyone else call it "bookmarks". Therefore the confusion.