Managing pages

Move and duplicate pages

Move changes the position of a page, and Insert with a page of the document inserts a copy of it (Duplicate inserts it after the page):

// Move the table of contents after the cover, and repeat the cover at the end
document.Pages.Move(2, 1);
document.Pages.Insert(document.Pages.Count, document.Pages[0]);

• A moved page keeps its object: the bookmarks, links and structure elements that go to it stay valid. A page that changes of node in the page tree of the file keeps its attributes: the resources, media box, crop box and rotation it inherited are copied to it first.
• A copy shares the content streams and the resources of its page. It has its annotations, except the form fields and the pop-up windows, and it is not tagged.
• A new page (Add) has the size it is created with: it does not inherit the rotation nor the crop box of the page tree.

Remove pages

RemoveAt removes a page and the references of the document to it, so that a full save does not write it anymore:

• the bookmarks and the links that go to the page lose their destination (they stay, without action);
• the named destinations of the page, and the open action that goes to it, are removed;
• its marked content and its annotations are removed from the structure tree;
• its form fields are removed from the form.

Merge documents

Add and Insert with a page of another document copy the page with the objects it uses:

public static byte[] Merge(IEnumerable<byte[]> files)
{
    var result = new PdfDocument();
    foreach (var file in files)
    {
        // The source documents must stay open until the result is saved
        var source = PdfDocument.Open(file);
        foreach (var page in source.Pages)
        {
            result.Pages.Add(page);
        }
    }

    return result.ToByteArray();
}

• The objects are renumbered in the target document. The objects that several pages of a source document use, such as the fonts and the images, are copied once.
• The source documents must stay open until the result is saved: the objects are read from them. An encrypted source is copied without its encryption: the result has the encryption of its own document.
• The links go to the copies of their pages, even when the page is imported after the link. A link to a page that is not imported has no destination; a named destination is replaced by the destination it names.
• The copies are not tagged, and their form fields are left out: the structure tree and the form belong to the source document.

Page boxes

The media box and the crop box are inherited from the page tree; the other boxes are not. A box must have finite coordinates. UserUnit is the size of the unit of the page in 1/72 inch: a value that is not a positive number is read as 1.

Draw on a rotated or cropped page

The coordinates of the content builder are those of the page before it is cropped and turned. To draw on the page as it is displayed, concatenate DisplayToUserSpace:

// Draw a stamp at the top-left corner of the page as it is displayed, whatever its rotation and crop box
var size = page.DisplaySize;
page.CreateContentBuilder()
    .Transform(page.DisplayToUserSpace)
    .DrawText("DRAFT", PdfFont.GetStandardFont(PdfStandardFont.HelveticaBold), 24, 20, size.Height - 40);

• In the display space, the origin is the lower-left corner of the page as it is displayed, y goes up, and the unit is 1/72 inch, whatever the UserUnit of the page. DisplaySize is the size of the page in that space.
• UserSpaceToDisplay goes the other way: transform the rectangle of an annotation with it to find where it is displayed.

Stamp a page on other pages

CreateFormFromPage makes a form XObject of the content of a page, of the document or of another one, to paint it as a letterhead, an overlay or an underlay:

// The page of another document becomes a form: painted on each page, under or over their content
var form = document.CreateFormFromPage(sourcePage);
foreach (var page in document.Pages)
{
    page.CreateContentBuilder().DrawForm(form);
}

The form is upright, with its lower-left corner at the origin and the size of the page as it is displayed, whatever the rotation of the page; paint it after a transformation to place it. It is stored once, however many pages paint it. The annotations of the page are not part of it.