Cant update a page

I am trying to update this page –

https://www.sightwordsgame.com/holidays-special-dates/winter/

When I add the following content to the table, it ignores it and reverts to the original version. I can put the same code in another page & it works.

<tr><td><a href="https://www.sightwordsgame.com/wp-content/uploads/2011/11/Winter-2.pdf"><img src="https://www.sightwordsgame.com/wp-content/uploads/2011/11/Winter-2.jpg" alt="Winter-2" width="185" height="240" class="alignnone size-full wp-image-21509" /></a></td>
<td><a href="https://www.sightwordsgame.com/wp-content/uploads/2011/11/Winter-3.pdf"><img src="https://www.sightwordsgame.com/wp-content/uploads/2011/11/Winter-3.jpg" alt="Winter-3" width="185" height="240" class="alignnone size-full wp-image-21510" /></a></td>
<td><a href="https://www.sightwordsgame.com/wp-content/uploads/2011/11/Winter-4.pdf"><img src="https://www.sightwordsgame.com/wp-content/uploads/2011/11/Winter-4.jpg" alt="Winter-4" width="185" height="240" class="alignnone size-full wp-image-21511" /></a></td></tr>