This article shows how to draw thumbnails with page number:

In PDFVCanvas class, add the following method:

-(void)DrawThumbBmp:(PDFDIB *)dib :(int)x :(int)y :(int)page
{
    NSString *opage = [NSString stringWithFormat:@"%i", page + 1];    

    Byte *data = (Byte *)[dib data];    int w = [dib width];
    int h = [dib height];

    CGDataProviderRef provider = CGDataProviderCreateWithData( NULL, data, w * h * 4, NULL );
    CGColorSpaceRef cs = CGColorSpaceCreateDeviceRGB();
    CGImageRef img = CGImageCreate( w, h, 8, 32, w<<2, cs, kCGBitmapByteOrder32Little|kCGImageAlphaNoneSkipFirst, provider, NULL, FALSE, kCGRenderingIntentDefault );
    CGColorSpaceRelease(cs);

    CGDataProviderRelease(provider);
    CGContextSaveGState(m_ctx);

    float tmp = 1/m_scale;
    CGContextTranslateCTM(m_ctx, x * tmp, (y + h) * tmp);
    CGContextScaleCTM(m_ctx, tmp, -tmp);
    CGContextDrawImage(m_ctx, CGRectMake(0, 0, w, h), img);

    // Add the page number
    NSMutableParagraphStyle *paragraphStyle = [[NSMutableParagraphStyle alloc] init];
    [paragraphStyle setAlignment:NSTextAlignmentCenter];

    CGContextTranslateCTM(m_ctx, 0.0f, h);
    CGContextScaleCTM(m_ctx, 1.0f, -1.0f);

    // Set font and color
    [opage drawInRect:CGRectMake(0, h/2 - h/5, w, h/5) withAttributes:@{NSFontAttributeName: [UIFont fontWithName:@"Helvetica" size:h/5], NSForegroundColorAttributeName: [UIColor colorWithRed:1.0f green:0.0f blue:0.0f alpha:1.0f], NSParagraphStyleAttributeName: paragraphStyle}];   

    CGContextRestoreGState(m_ctx);
    CGImageRelease(img);
}

Edit DrawThumb method of PDFVPage class to use the new method instead of DrawBmp:

-(void)DrawThumb:(PDFVCanvas *)canvas
{
    if( m_thumb != nil && [m_thumb Bmp] != nil )
        [canvas DrawThumbBmp:[m_thumb Bmp] :m_x :m_y :m_pageno]; // New method
    else
        [canvas FillRect: CGRectMake(m_x, m_y, m_w, m_h): 0xFFFFFFFF];

    if( m_sel != nil )
        [m_sel DrawSel:canvas: m_scale: [m_doc pageHeight:m_pageno]: m_x: m_y];
}