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@ -2,7 +2,7 @@ Changes in PDFio
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================
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v1.3.2 - YYYY-MM-DD
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v1.3.2 - 2024-08-15
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-------------------
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- Added some more sanity checks to the TrueType font reader.
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55
doc/pdfio.md
55
doc/pdfio.md
@ -118,20 +118,6 @@ that are defined in a separate header file:
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```c
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#include <pdfio-content.h>
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```
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API Overview
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============
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PDFio exposes several types:
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- `pdfio_file_t`: A PDF file (for reading or writing)
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- `pdfio_array_t`: An array of values
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- `pdfio_dict_t`: A dictionary of key/value pairs in a PDF file, object, etc.
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- `pdfio_obj_t`: An object in a PDF file
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- `pdfio_stream_t`: An object stream
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Understanding PDF Files
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-----------------------
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@ -286,40 +272,19 @@ startxref %startxref keyword
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%%EOF %End-of-file marker
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```
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How a PDF File is Read
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----------------------
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To read a PDF file, converting it from a flat series of bytes into a graph of objects in memory,
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the following steps might typically occur:
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1. Read the PDF header from the beginning of the file, checking that this is, indeed, a PDF
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document and retrieving its version number.
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3. The end-of-file marker is now found, by searching backward from the end of the file.
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The trailer dictionary can now be read, and the byte offset of the start of the cross-reference
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table retrieved.
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5. The cross-reference table can now be read. We now know where each object in the file is.
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6. At this stage, all the objects can be read and parsed, or we can leave this process until each
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object is actually needed, reading it on demand.
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8. We can now use the data, extracting the pages, parsing graphical content, extracting metadata,
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and so on.
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This is not an exhaustive description, since there are many possible complications
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(encryption, linearization, objects, and cross reference streams).
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API Overview
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============
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PDFio exposes several types:
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- `pdfio_file_t`: A PDF file (for reading or writing)
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- `pdfio_array_t`: An array of values
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- `pdfio_dict_t`: A dictionary of key/value pairs in a PDF file, object, etc.
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- `pdfio_obj_t`: An object in a PDF file
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- `pdfio_stream_t`: An object stream
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How a PDF File is Written
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-------------------------
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Writing a PDF document to a series of bytes in a file is much simpler than
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reading it—we don’t need to support all of the PDF format, just the subset
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we intend to use. Writing a PDF file is very fast, since it amounts to little
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more than flattening the object graph to a series of bytes.
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1. Output the header.
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2. Remove any objects which are not referenced by any other object in the
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PDF. This avoids writing objects which are no longer needed.
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3. Renumber the objects so they run from 1 to n where n is the number of
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objects in the file.
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4. Output the objects one by one, starting with object number one,
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recording the byte offset of each for the cross-reference table.
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5. Write the cross-reference table.
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6. Write the trailer, trailer dictionary, and end-of-file marker.
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Reading PDF Files
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-----------------
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