Getting validation error inside input type file using Angular.js

Question

I am facing an issue while selecting file using Angular.js. Here is my code:

<div ng-class="{'myError': billdata.compregdoc.$touched && billdata.compregdoc.$invalid }">
  <input type="file" 
         class="filestyle form-control" 
         data-size="lg" 
         name="compregdoc" 
         id="compregdoc" 
         ng-model="compregfile" 
         ngf-pattern="application/pdf,application/vnd.ms-powerpoint,application/vnd.openxmlformats-officedocument.wordprocessingml.document"
         accept="application/pdf,application/vnd.ms-powerpoint,application/vnd.openxmlformats-officedocument.wordprocessingml.document" 
         ngf-select="onCompRegFileSelect($file);" 
         ngf-max-size="2MB">

  <div style="clear:both;"></div>
</div>
</div>
<div class="help-block" 
     ng-messages="billdata.compregdoc.$error" 
     ng-if="billdata.compregdoc.$touched">

  <p ng-message="pattern" style="color:#F00;">This field only accepts .pdf,.ppt,.docx files.</p>
  <p ng-message="maxSize" style="color:#F00;">File is too large.Max size is 2 mb.</p>
</div>

In this case I am only able to upload pdf type file. But here I need pdf,ppt,docx,excel format file upload. When I am selecting the docx file it is showing me the validation message that This field only accepts .pdf,.ppt,.docx files.