akaunting/akaunting

{
    "name": "akaunting/akaunting",
    // ...
    "require": {
        "php": "^7.3.0",
        "ext-bcmath": "*",
        "akaunting/laravel-firewall": "^1.2",
        // ...

        "barryvdh/laravel-dompdf": "0.*",

        // ...
    },
}

// Controller method to download the PDF invoice
// It builds the PDF on the fly from the Blade View  

// Trait "Documents" is important, see its content below
use App\Traits\Documents;

class Invoices extends Controller
{
    use DateTime, Currencies, Documents, Uploads;

    public function pdfInvoice(Document $invoice, Request $request)
    {
        $view = view($invoice->template_path, compact('invoice', 'currency_style'))->render();
        $html = mb_convert_encoding($view, 'HTML-ENTITIES', 'UTF-8');

        $pdf = app('dompdf.wrapper');
        $pdf->loadHTML($html);

        $file_name = $this->getDocumentFileName($invoice);

        return $pdf->download($file_name);
    }
}

namespace App\Traits;

trait Documents
{
    // ... other methods

    public function getDocumentFileName(Document $document, string $separator = '-', string $extension = 'pdf'): string
    {
        return $this->getSafeDocumentNumber($document, $separator) . $separator . time() . '.' . $extension;
    }

    public function getSafeDocumentNumber(Document $document, string $separator = '-'): string
    {
        return Str::slug($document->document_number, $separator, language()->getShortCode());
    }
}

Route::group(['as' => 'portal.'], function () {
    // ... other routes
    Route::get('invoices/{invoice}/pdf', 'Portal\Invoices@pdfInvoice')->name('invoices.pdf');
});