diff --git a/citations-tools.php b/citations-tools.php
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--- /dev/null
+++ b/citations-tools.php
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+<?php
+/*
+Plugin Name: Citations tools
+Description: The plugin add some shortcodes add a link to a paper using the doi code or to resolve doi code and publish a full citation apa formatted.
+Version: 0.2.3
+Author: Gianluigi Filippelli
+Author URI: http://dropseaofulaula.blogspot.it/
+Plugin URI: 
+License: GPLv2 or later
+*/
+/* ------------------------------------------------------ */
+# ---------------------------------------------------------
+
+# doi
+add_shortcode('doi', 'doi');
+
+ function doi ($atts, $content = null) {
+
+   extract(
+      shortcode_atts(
+         array( 
+		'code' => null
+	 ),
+         $atts
+      )
+   );
+
+   $link = '<a href="https://dx.doi.org/'.$code.'/" target="doi">'.$content.'</a>';
+
+   return $link;
+}
+
+# doi resolve
+add_shortcode('doiresolve', 'doiresolve');
+
+ function doiresolve ($atts, $content = null) {
+
+  extract(
+      shortcode_atts(
+         array( 
+		'code' => null,
+                'arxiv' => null,
+                'pdfurl' => null
+	 ),
+         $atts
+      )
+   );
+
+   $fullCitation = null;
+   $getfile = 'https://search.crossref.org/dois?sort=score&page=1&rows=1&q='.$code;
+   $jsondata = file_get_contents($getfile);
+   $array = json_decode($jsondata,true);
+   $item=$array[0];
+   $doi = $item['doi'];
+   $coins = $item['coins'];
+   $fullCitation =$item['fullCitation'];
+
+   $citation = '<p>'.$fullCitation.' doi:<a href="https://dx.doi.org/'.$code.'" target="doi">'.$code.'</a>';
+
+   if ( $arxiv <> null )
+   {$citation = $citation.' (<a href="https://arxiv.org/abs/'.$arxiv.'" target="arxiv">arXiv</a>)';}
+   else
+   {$citation = $citation;}
+
+   if ( $pdfurl <> null )
+   {$citation = $citation.' (<a href="'.$pdfurl.'" target="pdf">pdf</a>)';}
+   else
+   {$citation = $citation;}
+
+   $results = $citation.'</p>';
+
+   return $results;
+}
+/* ------------------------------------------------------ */
diff --git a/readme.txt b/readme.txt
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+++ b/readme.txt
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+=== Citations tools ===
+Contributors: ulaulaman
+Tags: doi, citations, research
+Requires at least: 4.8.5
+Tested up to: 4.9.2
+Requires PHP: 7.0.18
+Stable tag: trunk
+License: GPLv2 or later
+License URI: http://www.gnu.org/licenses/gpl-2.0.html
+
+The plugin add some shortcodes add a link to a paper using the doi code or to resolve doi code and publish a full citation apa formatted.
+
+== Description ==
+Using the standard for doi link, the plugin introduce a shortcode in order to create a link to a paper provided by doi.
+How to use the shortcode:
+
+[doi code="..."]Title of the paper[/doi]
+
+Using the [crossref.org](https://www.crossref.org/) api, the plugin add also a shortcode that resolve a doi code and publish a full citation formatted using the apa standard.
+How to use the shortcode:
+
+[doiresolve code="..."]
+
+There are also two optional parameters:
+
+[doiresolve code="..." arxiv="..."]
+
+if the paper has an arXiv version
+
+[doiresolve code="..." pdfurl="..."]
+
+if the paper has a free pdf version
+
+== Installation ==
+1.  Extract the citations-tools.zip file and upload its contents to the /wp-content/plugins/ directory. Alternately, you can install directly from the Plugin directory within your WordPress Install.
+2. Activate the plugin through the "Plugins" menu in WordPress.
+3. Use the shortcode into your posts or pages.
+
+== Changelog ==
+0.2.3 add pdf link in doi resolver as ahortcode's parameter
+0.2.2 add arXiv link in doi resolver as shortcode's parameter
+0.2.1 add doi link in doi resolver
+0.2 add shortcode to resolve doi using code
+0.1 shortcode for doi link