Free online PDF to SRT converter

It appears that converting Adobe Portable Documents directly to SubRip Subtitles (.pdf to .srt conversion) is not possible; at least not without a simple workaround involving two main steps. 

First you will need to convert your PDF document to a plain text format, which can then be easily converted to SRT. To do so, you can use tools, such as Adobe Acrobat Reader. Make sure the text file is well formatted and the subtitles timings are correctly edited to avoid issues when converting the text file to SRT.

1. In Adobe Acrobat Reader go to "Tools" tab and select "Export PDF."
2. In the next window, select "Plain Text" and click on "Export."
3. Choose where to save your text file and click "Save."

In order to convert your text file to SRT format, use tools like Aegisub, which is a popular choice as it offers a user-friendly interface and a variety of features to make your SRT files look professional.

1. Load your text file in Aegisub.
2. Start by setting the start and end time for your first subtitle in the "Timing" section.
3. Then, type your subtitle in the "Text" box in the "Edit" section.
4. Repeat the process for all your subtitles. Remember to save your work regularly.
5. Once done, go to "File" and select "Export Subtitles" to save your SRT file.

Please be aware that the procedure may need manual editing to guarantee precise transcription and subtitles timing. The program listed above is a common option, although there are additional online solutions depending on your particular requirements. Keep in mind that the complexity and structure of the original PDF file have a significant impact on the conversion procedure. Be aware that converting PDF files containing images or complex layouts could produce text that is challenging to convert into an SRT file. Before starting the conversion, you might need to manually correct the wording in such circumstances.