C program for reading doc, docx, pdf - c

Question

I want to write a program in C(only c not c++ or java) that will read doc, docx, pdf and want to make it available on github to use for all who needs that code. So I started with .doc file I explored that if I open .doc file with simple notepad it will show you all text but just with some extra content which you can easily trim. So I did write a simple c program to read .doc wile in both 'r' and 'rb' mode but both time it gives me only 5-9 character in the file and those also not readable. I don't know why it's happening. Any comment or disccussion will be very helpful for me.
Here is the link for github Source code. Please help me to complete all three format.

Answer 1

To answer your specific question, the reason your little application stops reading is because it mistakenly thinks there is an EOF character in your file.
Look at your code:
char ch;
int nol=0, not=0, nob=0, noc=0;
FILE *fp;
fp = fopen("file.doc","rb");
while(1)
{
ch = fgetc(fp);
if(ch==EOF)
{
break;
}
You store the result of fgetc(fp) in a variable of type char, which is a single-byte variable. However, the result of fgetc is very purposefully "int", not "char".
fgetc always returns a positive result in the range 0 to 255, except for when you reach the end of the file in which case it returns EOF, which is often implemented as a -1 value.
If you read a byte of value 255 and store it in an int, everything is OK, it's stored as the value 255 and your loop can continue. If you store the result in a char, it's going to be interpreted equal to EOF. And your loop stops.

Answer 2

Don't expect to get anywhere with this idea. .doc is a huge binary file format that is inhumanly complicated to parse. With that said, Cubia mentioned the offset where the text section of the document starts. I'm not familiar with the details of the format, but if the raw text is contained in one location, use fseek to get at it and stop when you reach the end. This won't be the case for the other formats because they are very different.
.docx and .pdf should be easier to parse because they are more modern formats. If you want to read anything from a docx you need to read from a zip file with a ton of xml in it and use a parser to figure out which text you want.
.pdf should be the easiest of the three because you might be able to find a library out there that can almost do what you want.
As for why you are getting strange output from your program, remember that .doc is a binary format and the vast majority of the data is garbage from your perspective. Dumping it to the terminal will yield readable text but also a bunch of control characters that should screw with your terminal.
As a last note - don't try to read docx files directly using fread - they are compressed so you likely won't recover the text unaltered. Take a look at libarchive. Also - expect to have to read the document specifications. docx seems to be a microsoft extension to the openoffice format. See this and some PDF specification documents (there are multiple versions).

Answer 3

Look at the .doc file type as a txt file but with extra non-printable characters before, in the middle, and after your content. These non-printable characters are used for defining special formatting, metadata and other infos.
With this said, all .doc files follow a certain structure.
If you open two different .doc files in a hex editor, you will notice that the text content of both files start at an offset of 0xA00 (2560 bytes) from the beginning of the file. This means that when you open your file initially, you can ignore the first 2560 bytes of the file (Take a look at the fseek() function).
From this point on, you can read the contents of your file until you reach '\0'.
I have not seen the implementation of a .pdf or a .docx file, but you can take open up both files with a hex editor and figure out what pattern you can use the isolate the important contents of the files.
Hope this helps.
EDIT : You can always find documentation on the different file formats that you want to manipulate. Here are the specifications of the PDF file type :
http://www.adobe.com/devnet/pdf/pdf_reference.html
http://wwwimages.adobe.com/content/dam/Adobe/en/devnet/pdf/pdfs/PDF32000_2008.pdf