QUESTION: What is PDF?
ANSWER: PDF stands for Portable Document Format. It is a file format that describes the text and graphics in documents. It was invented by Adobe Systems Incorporated.
Because it describes the text and graphics in documents, PDF is considered to be a page-description language. Note, however, that PDF is quite different from other page-description languages (such as PostScript and PCL) because — unlike other page-description languages — PDF can do much more than simply describe the appearance of a document. See What is Adobe Acrobat? for more information about this.
Software that supports PDF viewing (such as the Adobe Acrobat software) understands the PDF format.
Here is an example of a PDF file:
%PDF-1.0
1 0 obj
<<
/Type /Catalog
/Pages 3 0 R
/Outlines 2 0 R
>>
endobj
2 0 obj
<<
/Type /Outlines
/Count 0
>>
endobj
3 0 obj
<<
/Type /Pages
/Count 1
/Kids [4 0 R]
>>
endobj
4 0 obj
<<
/Type /Page
/Parent 3 0 R
/Resources << /Font << /F1 7 0 R >>/ProcSet 6 0 R
>>
/MediaBox [0 0 612 792]
/Contents 5 0 R
>>
endobj
5 0 obj
<< /Length 129 >>
stream
BT
/F1 12 Tf
72 648 Td (Here is a line of text.) Tj
ET
endstream
endobj
6 0 obj
[/PDF /Text]
endobj
7 0 obj
<<
/Type /Font
/Subtype /Type1
/Name /F1
/BaseFont /Helvetica
/Encoding /MacRomanEncoding
>>
endobj
xref
0 8
0000000000 65535 f
0000000009 00000 n
0000000074 00000 n
0000000120 00000 n
0000000179 00000 n
0000000322 00000 n
0000000415 00000 n
0000000445 00000 n
trailer
<<
/Size 8
/Root 1 0 R
>>
startxref
553
%%EOF
The PDF file depicted above describes a one-page document with one line of text that is positioned one inch from the left edge of the page and nine inches from the bottom of the page.
The PDF file format is somewhat complex. If you'd like to understand it, you can read Adobe System's Incorporated's PDF Reference.