Reading a file

reader is the parsing and writing half: everything about the format itself, and nothing about what a page means.

d, err := reader.Open(bytes)          // or OpenWithPassword
fmt.Println(d.Version(), d.PageCount())

page, _ := d.Page(1)                  // with its inherited attributes
content, _ := d.PageContent(1)        // every stream, decoded and joined
ops, _ := d.PageOperations(1)         // and cut into operators

What it reads

Objects and the lexer; cross-reference tables and streams, hybrid files, /Prev chains and object streams; repair by scanning the file when the table is wrong; the filters — Flate, LZW (with and without early change), ASCIIHex, ASCII85, RunLength, and the PNG and TIFF predictors; the standard security handler from RC4-40 through AES-128 to AES-256 revision 6; content streams and inline images; the page tree with inherited attributes.

Document.Protection says how a file that opened was protected — the method in words, the handler's revision, what it allows, and whether the password it opened with was the owner's.

Writing

Writer produces a file, and produces the same bytes twice:

w := reader.NewPackedWriter("1.7")     // objects in compressed streams
pages := w.Reserve()
content := w.Add(&reader.Stream{Dict: reader.Dict{}, Raw: []byte("0 g 10 10 80 80 re f")})
page := w.Add(reader.Dict{"Type": reader.Name("Page"), "Parent": pages, "Contents": content})
w.Put(pages, reader.Dict{"Type": reader.Name("Pages"),
    "Kids": reader.Array{page}, "Count": reader.Integer(1)})
root := w.Add(reader.Dict{"Type": reader.Name("Catalog"), "Pages": pages})
out, _ := w.Finish(reader.Dict{"Root": root})

Writer.Encrypt protects everything written from there on, and Writer.Copy brings an object across from another document with everything it refers to.

What the corpus says

Of 118 863 files, 118 833 open. The thirty that do not are 27 PNGs named .pdf, one PostScript file, and two truncated past recovery.

1 536 769 753 content operations read across them, using 70 real operators. All 118 833 rewrite to an identical fingerprint, at 94.6% of the input size with the packed writer, and all 118 833 encrypt and decrypt in both AES methods.