lopdf

A Rust library for PDF document manipulation.

A useful reference for understanding the PDF file format and the eventual usage of this library is the PDF 1.7 Reference Document. The PDF 2.0 specification is available here.

Example Code

• Create PDF document

use lopdf::dictionary;
use lopdf::{Document, Object, Stream};
use lopdf::content::{Content, Operation};

// with_version specifes the PDF version this document complies with.
let mut doc = Document::with_version("1.5");
// Object IDs are used for cross referencing in PDF documents. `lopdf` helps keep track of them
// for us. They are simple integers.
// Calls to `doc.new_object_id` and `doc.add_object` return an object id

// pages is the root node of the page tree
let pages_id = doc.new_object_id();

// fonts are dictionaries. The type, subtype and basefont tags
// are straight out of the PDF reference manual
//
// The dictionary macro is a helper that allows complex
// key, value relationships to be represented in a simpler
// visual manner, similar to a match statement.
// Dictionary is linkedHashMap of byte vector, and object
let font_id = doc.add_object(dictionary! {
    // type of dictionary
    "Type" => "Font",
    // type of font, type1 is simple postscript font
    "Subtype" => "Type1",
    // basefont is postscript name of font for type1 font.
    // See PDF reference document for more details
    "BaseFont" => "Courier",
});

// font dictionaries need to be added into resource dictionaries
// in order to be used.
// Resource dictionaries can contain more than just fonts,
// but normally just contains fonts
// Only one resource dictionary is allowed per page tree root
let resources_id = doc.add_object(dictionary! {
    // fonts are actually triplely nested dictionaries. Fun!
    "Font" => dictionary! {
        // F1 is the font name used when writing text.
        // It must be unique in the document. It does not
        // have to be F1
        "F1" => font_id,
    },
});

// Content is a wrapper struct around an operations struct that contains a vector of operations
// The operations struct contains a vector of operations that match up with a particular PDF
// operator and operands.
// Reference the PDF reference for more details on these operators and operands.
// Note, the operators and operands are specified in a reverse order than they
// actually appear in the PDF file itself.
let content = Content {
    operations: vec![
        // BT begins a text element. it takes no operands
        Operation::new("BT", vec![]),
        // Tf specifies the font and font size. Font scaling is complicated in PDFs. Reference
        // the reference for more info.
        // The into() methods are defined based on their paired .from() methods (this
        // functionality is built into rust), and are converting the provided values into
        // An enum that represents the basic object types in PDF documents.
        Operation::new("Tf", vec!["F1".into(), 48.into()]),
        // Td adjusts the translation components of the text matrix. When used for the first
        // time after BT, it sets the initial text position on the page.
        // Note: PDF documents have Y=0 at the bottom. Thus 600 to print text near the top.
        Operation::new("Td", vec![100.into(), 600.into()]),
        // Tj prints a string literal to the page. By default, this is black text that is
        // filled in. There are other operators that can produce various textual effects and
        // colors
        Operation::new("Tj", vec![Object::string_literal("Hello World!")]),
        // ET ends the text element
        Operation::new("ET", vec![]),
    ],
};

// Streams are a dictionary followed by a sequence of bytes. What that sequence of bytes
// represents depends on context
// The stream dictionary is set internally to lopdf and normally doesn't
// need to be manually manipulated. It contains keys such as
// Length, Filter, DecodeParams, etc
//
// content is a stream of encoded content data.
let content_id = doc.add_object(Stream::new(dictionary! {}, content.encode().unwrap()));

// Page is a dictionary that represents one page of a PDF file.
// It has a type, parent and contents
let page_id = doc.add_object(dictionary! {
    "Type" => "Page",
    "Parent" => pages_id,
    "Contents" => content_id,
});

// Again, pages is the root of the page tree. The ID was already created
// at the top of the page, since we needed it to assign to the parent element of the page
// dictionary
//
// This is just the basic requirements for a page tree root object. There are also many
// additional entries that can be added to the dictionary if needed. Some of these can also be
// defined on the page dictionary itself, and not inherited from the page tree root.
let pages = dictionary! {
    // Type of dictionary
    "Type" => "Pages",
    // Vector of page IDs in document. Normally would contain more than one ID and be produced
    // using a loop of some kind
    "Kids" => vec![page_id.into()],
    // Page count
    "Count" => 1,
    // ID of resources dictionary, defined earlier
    "Resources" => resources_id,
    // a rectangle that defines the boundaries of the physical or digital media. This is the
    // "Page Size"
    "MediaBox" => vec![0.into(), 0.into(), 595.into(), 842.into()],
};

// using insert() here, instead of add_object() since the id is already known.
doc.objects.insert(pages_id, Object::Dictionary(pages));

// Creating document catalog.
// There are many more entries allowed in the catalog dictionary.
let catalog_id = doc.add_object(dictionary! {
    "Type" => "Catalog",
    "Pages" => pages_id,
});

// Root key in trailer is set here to ID of document catalog,
// remainder of trailer is set during doc.save().
doc.trailer.set("Root", catalog_id);
doc.compress();

// Store file in current working directory.
// Note: Line is excluded when running tests
if false {
    doc.save("example.pdf").unwrap();
}

• Merge PDF documents

use lopdf::dictionary;

use std::collections::BTreeMap;

use lopdf::content::{Content, Operation};
use lopdf::{Document, Object, ObjectId, Stream, Bookmark};

pub fn generate_fake_document() -> Document {
    let mut doc = Document::with_version("1.5");
    let pages_id = doc.new_object_id();
    let font_id = doc.add_object(dictionary! {
        "Type" => "Font",
        "Subtype" => "Type1",
        "BaseFont" => "Courier",
    });
    let resources_id = doc.add_object(dictionary! {
        "Font" => dictionary! {
            "F1" => font_id,
        },
    });
    let content = Content {
        operations: vec![
            Operation::new("BT", vec![]),
            Operation::new("Tf", vec!["F1".into(), 48.into()]),
            Operation::new("Td", vec![100.into(), 600.into()]),
            Operation::new("Tj", vec![Object::string_literal("Hello World!")]),
            Operation::new("ET", vec![]),
        ],
    };
    let content_id = doc.add_object(Stream::new(dictionary! {}, content.encode().unwrap()));
    let page_id = doc.add_object(dictionary! {
        "Type" => "Page",
        "Parent" => pages_id,
        "Contents" => content_id,
        "Resources" => resources_id,
        "MediaBox" => vec![0.into(), 0.into(), 595.into(), 842.into()],
    });
    let pages = dictionary! {
        "Type" => "Pages",
        "Kids" => vec![page_id.into()],
        "Count" => 1,
    };
    doc.objects.insert(pages_id, Object::Dictionary(pages));
    let catalog_id = doc.add_object(dictionary! {
        "Type" => "Catalog",
        "Pages" => pages_id,
    });
    doc.trailer.set("Root", catalog_id);

    doc
}

fn main() -> std::io::Result<()> {
    // Generate a stack of Documents to merge
    let documents = vec![
        generate_fake_document(),
        generate_fake_document(),
        generate_fake_document(),
        generate_fake_document(),
    ];

    // Define a starting max_id (will be used as start index for object_ids)
    let mut max_id = 1;
    let mut pagenum = 1;
    // Collect all Documents Objects grouped by a map
    let mut documents_pages = BTreeMap::new();
    let mut documents_objects = BTreeMap::new();
    let mut document = Document::with_version("1.5");

    for mut doc in documents {
        let mut first = false;
        doc.renumber_objects_with(max_id);

        max_id = doc.max_id + 1;

        documents_pages.extend(
            doc
                    .get_pages()
                    .into_iter()
                    .map(|(_, object_id)| {
                        if !first {
                            let bookmark = Bookmark::new(String::from(format!("Page_{}", pagenum)), [0.0, 0.0, 1.0], 0, object_id);
                            document.add_bookmark(bookmark, None);
                            first = true;
                            pagenum += 1;
                        }

                        (
                            object_id,
                            doc.get_object(object_id).unwrap().to_owned(),
                        )
                    })
                    .collect::<BTreeMap<ObjectId, Object>>(),
        );
        documents_objects.extend(doc.objects);
    }

    // Catalog and Pages are mandatory
    let mut catalog_object: Option<(ObjectId, Object)> = None;
    let mut pages_object: Option<(ObjectId, Object)> = None;

    // Process all objects except "Page" type
    for (object_id, object) in documents_objects.iter() {
        // We have to ignore "Page" (as are processed later), "Outlines" and "Outline" objects
        // All other objects should be collected and inserted into the main Document
        match object.type_name().unwrap_or("") {
            "Catalog" => {
                // Collect a first "Catalog" object and use it for the future "Pages"
                catalog_object = Some((
                    if let Some((id, _)) = catalog_object {
                        id
                    } else {
                        *object_id
                    },
                    object.clone(),
                ));
            }
            "Pages" => {
                // Collect and update a first "Pages" object and use it for the future "Catalog"
                // We have also to merge all dictionaries of the old and the new "Pages" object
                if let Ok(dictionary) = object.as_dict() {
                    let mut dictionary = dictionary.clone();
                    if let Some((_, ref object)) = pages_object {
                        if let Ok(old_dictionary) = object.as_dict() {
                            dictionary.extend(old_dictionary);
                        }
                    }

                    pages_object = Some((
                        if let Some((id, _)) = pages_object {
                            id
                        } else {
                            *object_id
                        },
                        Object::Dictionary(dictionary),
                    ));
                }
            }
            "Page" => {}     // Ignored, processed later and separately
            "Outlines" => {} // Ignored, not supported yet
            "Outline" => {}  // Ignored, not supported yet
            _ => {
                document.objects.insert(*object_id, object.clone());
            }
        }
    }

    // If no "Pages" object found abort
    if pages_object.is_none() {
        println!("Pages root not found.");

        return Ok(());
    }

    // Iterate over all "Page" objects and collect into the parent "Pages" created before
    for (object_id, object) in documents_pages.iter() {
        if let Ok(dictionary) = object.as_dict() {
            let mut dictionary = dictionary.clone();
            dictionary.set("Parent", pages_object.as_ref().unwrap().0);

            document
                    .objects
                    .insert(*object_id, Object::Dictionary(dictionary));
        }
    }

    // If no "Catalog" found abort
    if catalog_object.is_none() {
        println!("Catalog root not found.");

        return Ok(());
    }

    let catalog_object = catalog_object.unwrap();
    let pages_object = pages_object.unwrap();

    // Build a new "Pages" with updated fields
    if let Ok(dictionary) = pages_object.1.as_dict() {
        let mut dictionary = dictionary.clone();

        // Set new pages count
        dictionary.set("Count", documents_pages.len() as u32);

        // Set new "Kids" list (collected from documents pages) for "Pages"
        dictionary.set(
            "Kids",
            documents_pages
                    .into_iter()
                    .map(|(object_id, _)| Object::Reference(object_id))
                    .collect::<Vec<_>>(),
        );

        document
                .objects
                .insert(pages_object.0, Object::Dictionary(dictionary));
    }

    // Build a new "Catalog" with updated fields
    if let Ok(dictionary) = catalog_object.1.as_dict() {
        let mut dictionary = dictionary.clone();
        dictionary.set("Pages", pages_object.0);
        dictionary.remove(b"Outlines"); // Outlines not supported in merged PDFs

        document
                .objects
                .insert(catalog_object.0, Object::Dictionary(dictionary));
    }

    document.trailer.set("Root", catalog_object.0);

    // Update the max internal ID as wasn't updated before due to direct objects insertion
    document.max_id = document.objects.len() as u32;

    // Reorder all new Document objects
    document.renumber_objects();

     //Set any Bookmarks to the First child if they are not set to a page
    document.adjust_zero_pages();

    //Set all bookmarks to the PDF Object tree then set the Outlines to the Bookmark content map.
    if let Some(n) = document.build_outline() {
        if let Ok(x) = document.get_object_mut(catalog_object.0) {
            if let Object::Dictionary(ref mut dict) = x {
                dict.set("Outlines", Object::Reference(n));
            }
        }
    }

    document.compress();

    // Save the merged PDF
    // Store file in current working directory.
    // Note: Line is excluded when running tests
    if false {
        document.save("merged.pdf").unwrap();
    }

    Ok(())
}

• Modify PDF document

use lopdf::Document;

// For this example to work a parser feature needs to be enabled
#[cfg(any(feature = "pom_parser", feature = "nom_parser"))]
{
    let mut doc = Document::load("assets/example.pdf").unwrap();

    doc.version = "1.4".to_string();
    doc.replace_text(1, "Hello World!", "Modified text!");
    // Store file in current working directory.
    // Note: Line is excluded when running tests
    if false {
        doc.save("modified.pdf").unwrap();
    }
}

FAQ

• Why does the library keep everything in memory as high-level objects until finally serializing the entire document?

  Normally a PDF document won't be very large, ranging from tens of KB to hundreds of MB. Memory size is not a bottle neck for today's computer. By keeping the whole document in memory, stream length can be pre-calculated, no need to use a reference object for the Length entry, the resulting PDF file is smaller for distribution and faster for PDF consumers to process.

  Producing is a one-time effort, while consuming is many more.