Building a Simple PDF - PDF Explained - page 18

Graphical Content
The page contents stream contains a sequence of operators for placing text and graphics
on the page. It was linked to by the /Contents entry in the page dictionary.
A stream object consists of a dictionary followed by a raw data stream, containing a
series of PDF operands and operators. Normally, this would be compressed to reduce
file size, but we're typing it in manually, so we don't compress it. We must also specify
the length of the stream in bytes— pdftk will add the required /Length entry to the stream
dictionary for us.
4 0 obj The page contents stream
<< >>
stream Beginning of stream
1. 0. 0. 1. 50. 700. cm Position at (50, 700)
BT Begin text block
/F0 36. Tf Select /F0 font at 36pt
(Hello, World!) Tj Place the text string
ET End text block
endstream End of stream
endobj
The result of this stream of graphics operators on the page is shown in Figure 2-2 .
Catalog, Cross-Reference Table, and Trailer
The last part of the file starts with the document catalog , which is the root object of the
object graph. There follows the cross-reference table , which gives the byte offsets of
each object in the file. We'll have pdftk fill this in for us. There are two final lines: one
gives the byte offset of the start of the cross-reference table (we write 0 and pdftk will
replace it for us). Finally, the end-of-file marker %%EOF .
5 0 obj
<< /Type /Catalog The document catalog
/Pages 1 0 R Reference to the page list
>>
endobj
xref Start of cross-reference table, which we have missed out
0 6
trailer
<< /Size 6 Number of lines in cross-reference table (number of objects plus one)
/Root 5 0 R Reference to the document catalog
>>
startxref
0 Byte offset of start of xref table, which we have set to 0
%%EOF End of file marker
Now we're ready to put these pieces together.