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.
- 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();
}
}-
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.