FAQ

1. What's exactly the license of FPDF? Are there any usage restrictions?
2. When I try to create a PDF, a lot of weird characters show on the screen. Why?
3. I try to generate a PDF and IE displays a blank page. What happens?
4. I send parameters using the POST method and the values don't appear in the PDF.
5. When I use a PHP session, IE doesn't display my PDF any more but asks me to download it.
6. I try to display a PDF and Acrobat says "There was an error opening this document. There was a problem reading this document (110)".
7. I try to put a PNG in a PDF and Acrobat says "There was an error processing a page. A drawing error occurred".
8. I'd like to put my image in real size in the PDF. How can I convert pixels to mm?
9. I can't make line breaks work. I put \n in the string printed by MultiCell but it doesn't work.
10. I try to put the Euro symbol but it doesn't work.
11. I draw a frame with very precise dimensions, but when printed I notice some differences.
12. I'd like to use the whole surface of the page, but when printed I always have some margins. How can I get rid of them?
13. What's the limit of the file sizes I can generate with FPDF?
14. Can I modify a PDF with FPDF?
15. I'd like to make a search engine in PHP and index PDF files. Can I do it with FPDF?
16. Can I convert an HTML page to PDF with FPDF?
17. Can I concatenate PDF files with FPDF?
18. How can I activate the protections on a PDF? I'd like to prevent people from copying the text or modifying the document.


1. What's exactly the license of FPDF? Are there any usage restrictions?

FPDF is Freeware (it is stated at the beginning of the source file). There is no usage restriction. You may embed it freely in your application (commercial or not), with or without modification.

2. When I try to create a PDF, a lot of weird characters show on the screen. Why?

These "weird" characters are in fact the actual content of your PDF. This behaviour is a bug of IE. When it first receives an HTML page, then a PDF from the same URL, it displays it directly without launching Acrobat. This happens frequently during the development stage: on the least script error, an HTML page is sent, and after correction, the PDF arrives.
To solve the problem, simply quit and restart IE. You can also go to another URL and come back.
To avoid this kind of inconvenience during the development, you can generate the PDF directly to a file and open it through the explorer.

3. I try to generate a PDF and IE displays a blank page. What happens?

First of all, check that you send nothing to the browser after the PDF (not even a space or a carriage return). You can put an exit statement just after the call to the Output() method to be sure.
If it still doesn't work, it means you're a victim of the "blank page syndrome". IE used in conjunction with the Acrobat plug-in suffers from numerous bugs, in all versions. You should test your application with as many IE versions as possible (at least if you're on the Internet). The problem occurs mostly with the POST method, so it is advised to avoid it (all the more that it causes other problems, see the next question). The GET works better but may fail when the URL becomes too long: don't use a query string with more than 45 characters. However, a trick exists to exceed this limit: end the URL with .pdf, which deceives IE. If you use a formular, you can add a hidden field at the last position:

<INPUT TYPE="HIDDEN" NAME="ext" VALUE=".pdf">

The usage of PHP sessions also often causes trouble (avoid using HTTP headers preventing caching). See question 5 for a workaround.

To avoid all these problems in a reliable manner, two main techniques exist:

- Disable the plug-in and use Acrobat as a helper application. To do this, launch Acrobat; in the File menu, Preferences, General, uncheck the option "Web Browser Integration" (for Acrobat 5: Edit, Preferences, Options, "Display PDF in Browser"). Then, the next time you load a PDF in IE, it displays the dialog box "Open it" or "Save it to disk". Uncheck the option "Always ask before opening this type of file" and choose Open. From now on, PDF files will open automatically in an external Acrobat window.
The drawback of the method is that you need to alter the client configuration, which you can do in an intranet environment but not for the Internet.

- Use a redirection technique. It consists in generating the PDF in a temporary file on the server and redirect the client on it (by using JavaScript, not the Location HTTP header which also causes trouble). For instance, at the end of the script, you can put the following:

//Determine a temporary file name in the current directory
$file=basename(tempnam(getcwd(),'tmp'));
//Save PDF to file
$pdf->Output($file);
//JavaScript redirection
echo "<HTML><SCRIPT>document.location='getpdf.php?f=$file';</SCRIPT></HTML>";

Then create the getpdf.php file with this:

<?php
$f=$HTTP_GET_VARS['f'];
//Check file (don't skip it!)
if(substr($f,0,3)!='tmp' or strpos($f,'/') or strpos($f,'\\'))
    die('Incorrect file name');
if(!file_exists($f))
    die('File does not exist');
//Handle special IE request if needed
if($HTTP_ENV_VARS['USER_AGENT']=='contype')
{
    Header('Content-Type: application/pdf');
    exit;
}
//Output PDF
Header('Content-Type: application/pdf');
Header('Content-Length: '.filesize($f));
readfile($f);
//Remove file
unlink($f);
exit;
?>

This method works in most cases but IE6 can still experience trouble. The "ultimate" method consists in redirecting directly to the temporary file. The file name must therefore end with .pdf:

//Determine a temporary file name in the current directory
$file=basename(tempnam(getcwd(),'tmp'));
rename($file,$file.'.pdf');
$file.='.pdf';
//Save PDF to file
$pdf->Output($file);
//JavaScript redirection
echo "<HTML><SCRIPT>document.location='$file';</SCRIPT></HTML>";

This method turns the dynamic PDF into a static one and avoids all troubles. But you have to do some cleaning in order to delete the temporary files. For instance:

function CleanFiles($dir)
{
    //Delete temporary files
    $t=time();
    $h=opendir($dir);
    while($file=readdir($h))
    {
        if(substr($file,0,3)=='tmp' and substr($file,-4)=='.pdf')
        {
            $path=$dir.'/'.$file;
            if($t-filemtime($path)>3600)
                @unlink($path);
        }
    }
    closedir($h);
}

This function deletes all files of the form tmp*.pdf older than an hour in the specified directory. You may call it where you want, for instance in the script which generates the PDF.

Remark: it is necessary to open the PDF in a new window, as you can't go backwards due to the redirection.

4. I send parameters using the POST method and the values don't appear in the PDF.

It's a problem affecting some versions of IE (especially the first 5.5). See the previous question for the ways to work around it.

5. When I use a PHP session, IE doesn't display my PDF any more but asks me to download it.

It's a problem affecting some versions of IE. To work around it, add the following line before session_start():

session_cache_limiter('private');

or do a redirection as explained in question 3.

6. I try to display a PDF and Acrobat says "There was an error opening this document. There was a problem reading this document (110)".

This is a locale-related problem. The decimal separator is configured as a comma whereas the dot is necessary to produce valid PDF files. To use the correct setting, add the following line:

setlocale('LC_NUMERIC','C');

or, depending on your system configuration:

setlocale('LC_NUMERIC','en');

or

setlocale('LC_NUMERIC','en_US');

7. I try to put a PNG in a PDF and Acrobat says "There was an error processing a page. A drawing error occurred".

Acrobat 5 has a bug and is unable to display transparent monochrome images (i.e. with 1 bit per pixel). Remove transparency or save your image in 16 colors (4 bits per pixel) or more.

8. I'd like to put my image in real size in the PDF. How can I convert pixels to mm?

An image has no "real size". The dimension it is given in the document is arbitrary. Except if you want to impose a particular resolution (for instance 300 dpi), in which case the ratio between the pixel width and the resolution gives the dimension.

9. I can't make line breaks work. I put \n in the string printed by MultiCell but it doesn't work.

You have to enclose your string with double quotes, not single ones.

10. I try to put the Euro symbol but it doesn't work.

The standard fonts have the Euro character at position 128. You can define a constant like this for convenience:

define('EURO',chr(128));

11. I draw a frame with very precise dimensions, but when printed I notice some differences.

To respect dimensions, you have to uncheck the option "Fit to page" in the print dialog box.

12. I'd like to use the whole surface of the page, but when printed I always have some margins. How can I get rid of them?

All printers have physical margins (different depending on the model), it is therefore impossible to remove them and print on the totality of the paper.

13. What's the limit of the file sizes I can generate with FPDF?

There is no particular limit. There are some constraints however:

- The maximum memory size allocated to PHP scripts defaults to 8MB. For very big documents, especially with images, this limit may be reached (the file being built into memory). The parameter is configured in the php.ini file.

- The maximum execution time allocated defaults to 30 seconds. This limit can of course be easily reached. It is configured in php.ini and may be altered dynamically with set_time_limit().

- Browsers generally have a 5 minute time-out. If you send the PDF directly to the browser and reach the limit, it will be lost. It is therefore advised for very big documents to generate them in a file, and to send some data to the browser from time to time (for instance page 1, page 2... with flush() to force the output). When the document is finished, you can send a redirection on it with JavaScript or create a link.
Remark: even when the browser goes in time-out, the script generally continues to run on the server.

14. Can I modify a PDF with FPDF?

No. There will be (I hope) a version in the future which will allow to import the content of a PDF and add elements to it.

15. I'd like to make a search engine in PHP and index PDF files. Can I do it with FPDF?

No. But a C utility does exist, pdftotext, which is able to extract the textual content from a PDF. It is provided with the Xpdf package.

http://www.foolabs.com/xpdf/

16. Can I convert an HTML page to PDF with FPDF?

No. But a C utility does exist, htmldoc, which allows to do it and gives good results.

http://www.easysw.com/htmldoc/

17. Can I concatenate PDF files with FPDF?

No.

18. How can I activate the protections on a PDF? I'd like to prevent people from copying the text or modifying the document.

You can't for the moment. Protecting a PDF requires to crypt it, and the algorithm used (RC4) is theoretically not free (even if this issue seems to be a little fuzzy and the algorithm might be tolerated for a non-commercial usage).