manual encryption pdf file base pdf 32000-2008

hi all

At First special thanks to “lrosenth” and “Test Screen Name” for the good answers in the previous threads 

Now I have another question

In PDF32000_2008 explained pdf syntax considered as a four part

1. 1) Objects
2. 2) File structure - - -> use this for encryption
3. 3) Document structure
4. 4) Content stream

Also mention that:  “we have 8 object types “

1) Boolean

2) Numeric

3) String

4) Name

5) Array

6) Stream

7) Null

8) Indirect

This object have a structure like this:

5 0 obj

<< /Type /XObject

/Subtype /Image

/Width 52

/Height 66

/ColorSpace /DeviceGray

/BitsPerComponent 1

/Length 224

/Filter [/ASCIIHexDecode /JBIG2Decode]

/DecodeParms [null << /JBIG2Globals 6 0 R >>]

>>

stream

000000013000010000001300000034000000420000000000

00000040000000000002062000010000001e000000340000

004200000000000000000200100000000231db51ce51ffac>

endstream

endobj

6 0 obj

<< /Length 126

/Filter /ASCIIHexDecode

>>

stream

0000000000010000000032000003fffdff02fefefe000000

01000000012ae225aea9a5a538b4d9999c5c8e56ef0f872

7f2b53d4e37ef795cc5506dffac>

endstream

endobj

In encryption section mention that we can encrypt string, streams, … .

As I think and understand for encryption I must extract encrypt able objects, for this goal I do this steps

ASFileSys fileSys = ASGetDefaultFileSysForPath(pathType, myPath);

       ASPathName pathName = ASFileSysCreatePathName(fileSys, pathType, myPath, NULL);

       AVDoc myAVDoc=AVDocOpenFromFile(pathName, fileSys, titleText);      

       PDDoc myPDDoc2 =AVDocGetPDDoc(myAVDoc);

       CosDoc cdoc;

       cdoc = PDDocGetCosDoc(myPDDoc2);

       CosObj cosOBJ=CosDocGetRoot(cdoc);

       CosType t = CosObjGetType(cosOBJ);

// traverse pdf file structure tree

       CosObj obj2= CosDictGet(cosOBJ,ASAtomFromString("Pages"));

       CosType ttt = CosObjGetType(obj2);

       CosObj obj3= CosDictGet(obj2,ASAtomFromString("Kids"));

       CosType tttt = CosObjGetType(obj3);

       CosObj kid1 = CosArrayGet(obj3,0);

       CosType tttrtt = CosObjGetType(kid1);

       CosObj cosst = CosDictGet(kid1,ASAtomFromString("Contents"));

       CosType ttrrrttt = CosObjGetType(cosst);

       ASArraySize s = CosStreamLength(cosst);

       ASStm stm= CosStreamOpenStm(cosst,2);

       char buf[10000];

       int aaaaagyg=ASStmRead(buf,1,10000,stm);

       ASStmFlush(stm);

       ASStmClose(stm);

Now in buf I have content like this

/CS0 cs 1  scn

10 36 591.75 729.75 re

f

BT

0  scn

/TT0 1 Tf

12 0 0 12 16 749.25 Tm

(a b c)Tj

0 -1.125 TD

(d e)Tj

T*

(f)Tj

ET

I thinked with ASStmWrite  can write in this and change pdf content but this is not possible ,

Then this is my questions

Are this steps are correct or not ?

If yes how I can extract encrypt able object and after edit save them as pdf file.

else I think I must use Crypt Filter.

how I can get dictionary and change parameters for example set V value to 4

how I can retrieve pdf object (like example I mention before (5 0 obj ….) )

if need to make Crypt Filter how do this ?

for make Crypt Filter need to edit encryption dictionary,  how edit encryption dictionary?

I really thankful for your guidance and time you spend for answer my questions

Regard F.Afshari