Update pdfio.md

doc/pdfio.md

@@ -146,13 +146,16 @@ Since PDF files almost always contain binary data, they can become corrupted if
 - For example: %âãÏÓ
 - The percent sign indicates another header line, the other few bytes are arbitrary character codes in excess of 127. So, the whole header in our example is:
 
+```
 %PDF-1.0  
 %âãÏÓ
+```
 
 ### Body
 The file body consists of a sequence of objects, each preceded by an object number, generation number, and the obj keyword on one line, and followed by the endobj keyword on another.
 - For Example:
-'''
+
+```  
 1 0 obj
 <<
 /Kids [2 0 R]
@@ -160,8 +163,10 @@ The file body consists of a sequence of objects, each preceded by an object numb
 /Type /Pages
 >>
 endobj
-'''
-- Here, the object number is 1, and the generation number is 0 (it almost always is). The content for object 1 is in between the two lines 1 0 obj and endobj. In this case, it’s the dictionary <</Kids [2 0 R] /Count 1 /Type /Pages>>
+```
+
+Here, the object number is 1, and the generation number is 0 (it almost always is). The content for object 1 is in between the two lines 1 0 obj and endobj.  
+In this case, it’s the dictionary <</Kids [2 0 R] /Count 1 /Type /Pages>>
 
 ### Cross-Reference Table
 The cross-reference table lists the byte offset of each object in the file body.
@@ -171,34 +176,35 @@ Operations like counting the number of pages in a PDF document are fast, even in
 Each object has an object number and a generation number.
   - Generation numbers are used when a cross-reference table entry is reused.
   - For simplicity, we would assume generation numbers to be always zero and ignore them.  
-- The cross-reference table consists of:
+The cross-reference table consists of:
   - Header line that indicates the number of entries.
   - Special entry (the first entry).
   - One line for each of the object in the file body.
 
-'''
-**0 6 Six entries in table, starting at 0**
-0000000000 65535 **f Special entry**
-0000000015 00000 **n Object 1 is at byte offset 15**
-0000000074 00000 **n Object 2 is at byte offset 74**
-0000000192 00000 **n etc...**
-0000000291 00000 **n**
-0000000409 00000 **n Object 5 is at byte offset 409**
-'''
+```
+0 6                **Six entries in table, starting at 0**
+0000000000 65535   **f Special entry**
+0000000015 00000   **n Object 1 is at byte offset 15**
+0000000074 00000   **n Object 2 is at byte offset 74**
+0000000192 00000   **n etc...**
+0000000291 00000   **n**
+0000000409 00000   **n Object 5 is at byte offset 409**
+```
 
 ### Trailer
 - The first line of the trailer is just the trailer keyword. This is followed by the trailer dictionary, which contains at least the /Size entry (which gives the number of entries in the cross-reference table) and the /Root entry (which gives the object number of the document catalog, which is the root element of the graph of objects in the body).
 - There follows a line with just the startxref keyword, a line with a single number (the byte offset of the start of the cross-reference table within the file), and then the line %%EOF, which signals the end of the PDF file.
-'''
-trailer **Trailer keyword**
-<< **The trailer dictinonary**
+
+```
+trailer        **Trailer keyword**
+<<             **The trailer dictinonary**
 /Root 5 0 R
 /Size 6
 >>
-startxref **startxref keyword**
-459 **Byte offset of cross-reference table**
-%%EOF **End-of-file marker**
-'''
+startxref      **startxref keyword**
+459            **Byte offset of cross-reference table**
+%%EOF          **End-of-file marker**
+```
 
 Reading PDF Files
 -----------------