Digitally signing a document

[driessen]

Hello,

A PDF-document can be signed digitally in Acrotbat Reader.

But does anyone know how I can check in my FWH-application if a PDF-document has been signed digitally?

Thank you in advance.

[Antonio Linares]

Dear Michel,

Asking chatgpt:

you can utilize a C library that provides PDF parsing capabilities. One such library is Poppler, which is widely used for working with PDF files in C

You can download the pre-built Poppler library for Windows from the Poppler website: https://poppler.freedesktop.org/.

Here is the code to check for the signature:

Code: Select all  Expand view

#include <stdio.h>
#include <poppler-document.h>

int main(int argc, char *argv[]) {
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <input_pdf>\n", argv[0]);
        return 1;
    }

    const char *input_pdf = argv[1];
    GError *error = NULL;

    // Open the PDF document
    PopplerDocument *document = poppler_document_new_from_file(input_pdf, NULL, &error);
    if (error != NULL) {
        fprintf(stderr, "Error opening PDF: %s\n", error->message);
        g_error_free(error);
        return 1;
    }

    // Check if the document is encrypted
    if (poppler_document_get_n_pages(document) == 0) {
        printf("The PDF is encrypted.\n");
    } else {
        printf("The PDF is not encrypted.\n");
    }

    // Check if the document is signed
    if (poppler_document_get_metadata(document, "signature") != NULL) {
        printf("The PDF is signed.\n");
    } else {
        printf("The PDF is not signed.\n");
    }

    // Free the document object
    g_object_unref(document);

    return 0;
}
 

We can easily adap that code to Harbour or simply build an EXE from it and run it

[driessen]

Antonio,

I'm afraid that is somewhat to difficult for me.
I need to know if a document is digitally signed or not.
But I don't know how to implement your suggestion.

[Horizon]

Antonio,

I'm afraid that is somewhat to difficult for me.
I need to know if a document is digitally signed or not.
But I don't know how to implement your suggestion.

Can you please send a link here a sample digitally signed pdf?

[Antonio Linares]

Much simpler

Use this function:

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#include "FiveWin.ch"

function Main()

    MsgInfo( IsSigned( "fwintro.pdf" ) )

return nil

function IsSigned( cPDFFileName )

return At( "/SigFlags", hb_memoRead( cPDFFileName ) ) != 0

[driessen]

Antonio,

Thanks a lot for your help.

I'll test it tonight or tomorrow.

Have a fine Sunday.

[driessen]

Antonio,

Unfortunately, I always get a .F. as result, whether it is signed or not.

[Antonio Linares]

Dear Michel,

Then I guess your PDFs are encrypted

Could you please email me one of them ? thanks

[driessen]

Antonio,

I just send you a PDF-file which I digitally signed.

The PDF-file was made by saving as a PDF-file in Word.

Thanks.

[Antonio Linares]

Dear Michel,

I got it, thank you

Do you also need to know information about the signature ?

[driessen]

No, I just need to know if the document is digitally signed or not.

[driessen]

FYI, Antonio,

If I use "Michel" in stead of "/SigFlags", I get a .T.

[Antonio Linares]

Dear Michel,

The simplest way I have found to build a tool to check if a PDF is signed is using python.

signed.py

Code: Select all  Expand view

import sys, aspose.pdf as ap

pdfSign = ap.facades.PdfFileSignature()
pdfSign.bind_pdf(sys.argv[ 1 ])
signatures = pdfSign.get_sign_names( True )

if( signatures.length ) > 0 :
   print( "signed" )
else:
   print( "not signed" )

Using pyinstaller we can create a standalone EXE:

Code: Select all  Expand view

pyinstaller --onefile signed.py

Here you have it:
https://wormhole.app/QoPx3#Ze8o1phu14n66ZQUwCH6TA

You can call it from FWH using:

Code: Select all  Expand view

WaitRun( "signed.exe " + cPdfFileName + " > result.txt" )
if hb_memoRead( "result.txt" ) == "signed"
   MsgInfo( "signed" )
else
   MsgInfo( "non signed" )
endif
 

Unfortunately signed.exe size is large but it works fine

[toninhofwi]

Hi, maybe you can test with chilkat:

https://www.example-code.com/foxpro/pdf_signatures.asp

Regards,

Toninho.

[Antonio Linares]

Great web for examples!

thank you