Depending on the number of files you're wanting to redirects it may be quicker to implement those at the server level (web.config file)
<system.webServer>
...
<rewriteMaps name="pdfRedirects" defaultValue="">
<add key="/old/site/file/path.pdf" value="/new/site/file/path.pdf" />
<add key="/old/site/file/path-another.pdf" value="/new/site/file/path-another.pdf" />
...
</rewriteMaps>
<rewrite>
<rules>
<rule name="PDF Redirect Rule" stopProcessing="true">
<match url="(.*)"/>
<conditions>
<add input="{pdfRedirects:{REQUEST_URI}}" pattern="(.+)"/>
</conditions>
<action type="Redirect" url="https://{HTTP_HOST}{C:1}" appendQueryString="false" redirectType="Permanent" />
</rule>
...
</rules>
</rewrite>
</system.webServer>