Disable PDF thumbnail generation

I have a Runway collection template which includes a repeater for attaching files:

...

<perch:repeater id="product_literature" label="Product Literature" divider-before="Attached Documents">
    <!--* ENGLISH *-->
    <perch:content id="en_title" type="text" label="Title (English)" divider-before="Language: English" />
    <perch:content id="en_file" type="file" bucket="Literature" label="File (English)" divider-after="EndLang" />
    <!--* CHINESE *-->
    <perch:content id="zh_title" type="text" label="Title (Chinese)" divider-before="Language: Chinese" />
    <perch:content id="zh_file" type="file" bucket="Literature" label="File (Chinese)" divider-after="EndLang" />
    <!--* FRENCH *-->
    <perch:content id="fr_title" type="text" label="Title (French)" divider-before="Language: French" />
    <perch:content id="fr_file" type="file" bucket="Literature" label="File (French)" divider-after="EndLang" />
    <!--* SPANISH *-->
    <perch:content id="es_title" type="text" label="Title (Spanish)" divider-before="Language: Spanish" />
    <perch:content id="es_file" type="file" bucket="Literature" label="File (Spanish)" divider-after="EndLang" />
    <!--* PORTUGUESE *-->
    <perch:content id="pt_title" type="text" label="Title (Portuguese)" divider-before="Language: Portuguese" />
    <perch:content id="pt_file" type="file" bucket="Literature" label="File (Portuguese)" divider-after="EndLang" />
</perch:repeater>

...

In some cases, 15+ PDFs may be attached to this repeater at once. I've noticed that saving can take a long time if there are multiple PDFs attached, which I assume is due to the thumbnail generation for these files. I have no need for these thumbnails. Is it possible to disable PDF thumbnail generation?

Diagnostics:

HEALTH CHECK

Perch Runway is up to date
PHP 5.6.14-1+deb.sury.org~trusty+1 is up to date
MySQL 5.5.46-0ubuntu0.14.04.2 is up to date
Image processing available
SUMMARY INFORMATION

Perch Runway: 2.8.31, PHP: 5.6.14-1+deb.sury.org~trusty+1, MySQL: mysqlnd 5.0.11-dev - 20120503 - $Id: 3c688b6bbc30d36af3ac34fdd4b7b5b787fe5555 $, with PDO
Server OS: Linux, apache2handler
Installed apps: content (2.8.31), assets (2.8.31), categories (2.8.31), perch_blog (5.0), perch_events (1.9.3), perch_forms (1.8.3)
App runtimes: <?php $apps_list = array( 'content', 'categories', 'perch_blog', 'perch_events', 'perch_forms', );
PERCH_LOGINPATH: /at-admin
PERCH_PATH: /var/www/public/axletech.dev/at-admin
PERCH_CORE: /var/www/public/axletech.dev/at-admin/core
PERCH_RESFILEPATH: /var/www/public/axletech.dev/at-admin/resources
Image manipulation: GD Imagick
PHP limits: Max upload 100M, Max POST 100M, Memory: 128M, Total max file upload: 100M
F1: 2edba60ed1f613d6dd804feb202456a2
Resource folder writeable: Yes
HTTP_HOST: axletech.dev
DOCUMENT_ROOT: /var/www/public/axletech.dev
REQUEST_URI: /at-admin/core/settings/diagnostics/
SCRIPT_NAME: /at-admin/core/settings/diagnostics/index.php